FA-76561 / Email MIME structure / Open access

Choose the MIME skeleton for an outgoing message: alternative order · case 01

The plain-text alternative is placed after the HTML one, so clients prefer plain text.

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ROOT CAUSE

The alternative order decision evaluates `'alternative(' + html + ',text)'` where the contract requires `'alternative(text,' + html + ')'`.

VERIFIED REPAIR

Use `'alternative(text,' + html + ')'` for the alternative order decision and keep every other rule of the model unchanged.

Unsuccessful approach: Fixing the order only for messages without images keeps the wrong order when images are present. The attempted `'alternative(' + html + ',text)' if inline_images else 'alternative(text,' + html + ')'` still disagrees with a fixture.

Case contract

The body is multipart/alternative(text, html) when both versions exist, the html alone when only html exists, else text. Inline images go into multipart/related with the html root first; without html they become attachments. When there are attachments the result is multipart/mixed(body, attachments...). Output is a compact string such as "mixed(alternative(text,related(html,img)),att)".

Why this case matters

Composing the wrong skeleton makes clients show images as attachments, hide the plain-text version or drop parts.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(has_text, has_html, inline_images, attachments):
    atts = attachments
    html = None
    if has_html:
        html = 'html' if inline_images == 0 else 'related(' + ','.join(['html'] + ['img'] * inline_images) + ')'
    else:
        atts += inline_images
    if has_text and html:
        body = 'alternative(' + html + ',text)'
    elif html:
        body = html
    else:
        body = 'text'
    if atts:
        return 'mixed(' + ','.join([body] + ['att'] * atts) + ')'
    return body
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_CASES = {1: [('images without html', (False, False, 2, 0), 'mixed(text,att,att)'), ('text and html', (True, True, 0, 0), 'alternative(text,html)'), ('text html and images', (True, True, 2, 0), 'alternative(text,related(html,img,img))'), ('html images and attachment', (False, True, 1, 1), 'mixed(related(html,img),att)'), ('text and attachments', (True, False, 0, 1), 'mixed(text,att)'), ('plain text only', (True, False, 0, 0), 'text'), ('everything', (True, True, 2, 1), 'mixed(alternative(text,related(html,img,img)),att)')], 2: [('images without html', (False, False, 3, 0), 'mixed(text,att,att,att)'), ('text and html', (True, True, 0, 0), 'alternative(text,html)'), ('text html and images', (True, True, 3, 0), 'alternative(text,related(html,img,img,img))'), ('html images and attachment', (False, True, 2, 1), 'mixed(related(html,img,img),att)'), ('text and attachments', (True, False, 0, 2), 'mixed(text,att,att)'), ('plain text only', (True, False, 0, 0), 'text'), ('everything', (True, True, 2, 2), 'mixed(alternative(text,related(html,img,img)),att,att)')], 3: [('images without html', (False, False, 4, 0), 'mixed(text,att,att,att,att)'), ('text and html', (True, True, 0, 0), 'alternative(text,html)'), ('text html and images', (True, True, 4, 0), 'alternative(text,related(html,img,img,img,img))'), ('html images and attachment', (False, True, 3, 1), 'mixed(related(html,img,img,img),att)'), ('text and attachments', (True, False, 0, 3), 'mixed(text,att,att,att)'), ('plain text only', (True, False, 0, 0), 'text'), ('everything', (True, True, 2, 3), 'mixed(alternative(text,related(html,img,img)),att,att,att)')], 4: [('images without html', (False, False, 5, 0), 'mixed(text,att,att,att,att,att)'), ('text and html', (True, True, 0, 0), 'alternative(text,html)'), ('text html and images', (True, True, 5, 0), 'alternative(text,related(html,img,img,img,img,img))'), ('html images and attachment', (False, True, 4, 1), 'mixed(related(html,img,img,img,img),att)'), ('text and attachments', (True, False, 0, 4), 'mixed(text,att,att,att,att)'), ('plain text only', (True, False, 0, 0), 'text'), ('everything', (True, True, 2, 4), 'mixed(alternative(text,related(html,img,img)),att,att,att,att)')], 5: [('images without html', (False, False, 6, 0), 'mixed(text,att,att,att,att,att,att)'), ('text and html', (True, True, 0, 0), 'alternative(text,html)'), ('text html and images', (True, True, 6, 0), 'alternative(text,related(html,img,img,img,img,img,img))'), ('html images and attachment', (False, True, 5, 1), 'mixed(related(html,img,img,img,img,img),att)'), ('text and attachments', (True, False, 0, 5), 'mixed(text,att,att,att,att,att)'), ('plain text only', (True, False, 0, 0), 'text'), ('everything', (True, True, 2, 5), 'mixed(alternative(text,related(html,img,img)),att,att,att,att,att)')]}
for _label, _args, _expected in _CASES[N]:
    check(_label, solve(*_args), _expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
images without html	`mixed(text,att,att)`	`mixed(text,att,att)`	Passed
text and html	`alternative(html,text)`	`alternative(text,html)`	Failed
text html and images	`alternative(related(html,img,img),text)`	`alternative(text,related(html,img,img))`	Failed
html images and attachment	`mixed(related(html,img),att)`	`mixed(related(html,img),att)`	Passed
text and attachments	`mixed(text,att)`	`mixed(text,att)`	Passed
plain text only	`text`	`text`	Passed
everything	`mixed(alternative(related(html,img,img),text),att)`	`mixed(alternative(text,related(html,img,img)),att)`	Failed

SHA-256 / 5f4a370f3b1725a3de0934f7199c8f054ac2dabefcb5973d856cddc8de82cf87

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(has_text, has_html, inline_images, attachments):
    atts = attachments
    html = None
    if has_html:
        html = 'html' if inline_images == 0 else 'related(' + ','.join(['html'] + ['img'] * inline_images) + ')'
    else:
        atts += inline_images
    if has_text and html:
        body = 'alternative(' + html + ',text)' if inline_images else 'alternative(text,' + html + ')'
    elif html:
        body = html
    else:
        body = 'text'
    if atts:
        return 'mixed(' + ','.join([body] + ['att'] * atts) + ')'
    return body
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_CASES = {1: [('images without html', (False, False, 2, 0), 'mixed(text,att,att)'), ('text and html', (True, True, 0, 0), 'alternative(text,html)'), ('text html and images', (True, True, 2, 0), 'alternative(text,related(html,img,img))'), ('html images and attachment', (False, True, 1, 1), 'mixed(related(html,img),att)'), ('text and attachments', (True, False, 0, 1), 'mixed(text,att)'), ('plain text only', (True, False, 0, 0), 'text'), ('everything', (True, True, 2, 1), 'mixed(alternative(text,related(html,img,img)),att)')], 2: [('images without html', (False, False, 3, 0), 'mixed(text,att,att,att)'), ('text and html', (True, True, 0, 0), 'alternative(text,html)'), ('text html and images', (True, True, 3, 0), 'alternative(text,related(html,img,img,img))'), ('html images and attachment', (False, True, 2, 1), 'mixed(related(html,img,img),att)'), ('text and attachments', (True, False, 0, 2), 'mixed(text,att,att)'), ('plain text only', (True, False, 0, 0), 'text'), ('everything', (True, True, 2, 2), 'mixed(alternative(text,related(html,img,img)),att,att)')], 3: [('images without html', (False, False, 4, 0), 'mixed(text,att,att,att,att)'), ('text and html', (True, True, 0, 0), 'alternative(text,html)'), ('text html and images', (True, True, 4, 0), 'alternative(text,related(html,img,img,img,img))'), ('html images and attachment', (False, True, 3, 1), 'mixed(related(html,img,img,img),att)'), ('text and attachments', (True, False, 0, 3), 'mixed(text,att,att,att)'), ('plain text only', (True, False, 0, 0), 'text'), ('everything', (True, True, 2, 3), 'mixed(alternative(text,related(html,img,img)),att,att,att)')], 4: [('images without html', (False, False, 5, 0), 'mixed(text,att,att,att,att,att)'), ('text and html', (True, True, 0, 0), 'alternative(text,html)'), ('text html and images', (True, True, 5, 0), 'alternative(text,related(html,img,img,img,img,img))'), ('html images and attachment', (False, True, 4, 1), 'mixed(related(html,img,img,img,img),att)'), ('text and attachments', (True, False, 0, 4), 'mixed(text,att,att,att,att)'), ('plain text only', (True, False, 0, 0), 'text'), ('everything', (True, True, 2, 4), 'mixed(alternative(text,related(html,img,img)),att,att,att,att)')], 5: [('images without html', (False, False, 6, 0), 'mixed(text,att,att,att,att,att,att)'), ('text and html', (True, True, 0, 0), 'alternative(text,html)'), ('text html and images', (True, True, 6, 0), 'alternative(text,related(html,img,img,img,img,img,img))'), ('html images and attachment', (False, True, 5, 1), 'mixed(related(html,img,img,img,img,img),att)'), ('text and attachments', (True, False, 0, 5), 'mixed(text,att,att,att,att,att)'), ('plain text only', (True, False, 0, 0), 'text'), ('everything', (True, True, 2, 5), 'mixed(alternative(text,related(html,img,img)),att,att,att,att,att)')]}
for _label, _args, _expected in _CASES[N]:
    check(_label, solve(*_args), _expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
images without html	`mixed(text,att,att)`	`mixed(text,att,att)`	Passed
text and html	`alternative(text,html)`	`alternative(text,html)`	Passed
text html and images	`alternative(related(html,img,img),text)`	`alternative(text,related(html,img,img))`	Failed
html images and attachment	`mixed(related(html,img),att)`	`mixed(related(html,img),att)`	Passed
text and attachments	`mixed(text,att)`	`mixed(text,att)`	Passed
plain text only	`text`	`text`	Passed
everything	`mixed(alternative(related(html,img,img),text),att)`	`mixed(alternative(text,related(html,img,img)),att)`	Failed

SHA-256 / fce8b320ffd51a22394ac19f0ce9e2b97dfe7e980c7239e9330edad8ca5b030c

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(has_text, has_html, inline_images, attachments):
    atts = attachments
    html = None
    if has_html:
        html = 'html' if inline_images == 0 else 'related(' + ','.join(['html'] + ['img'] * inline_images) + ')'
    else:
        atts += inline_images
    if has_text and html:
        body = 'alternative(text,' + html + ')'
    elif html:
        body = html
    else:
        body = 'text'
    if atts:
        return 'mixed(' + ','.join([body] + ['att'] * atts) + ')'
    return body
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_CASES = {1: [('images without html', (False, False, 2, 0), 'mixed(text,att,att)'), ('text and html', (True, True, 0, 0), 'alternative(text,html)'), ('text html and images', (True, True, 2, 0), 'alternative(text,related(html,img,img))'), ('html images and attachment', (False, True, 1, 1), 'mixed(related(html,img),att)'), ('text and attachments', (True, False, 0, 1), 'mixed(text,att)'), ('plain text only', (True, False, 0, 0), 'text'), ('everything', (True, True, 2, 1), 'mixed(alternative(text,related(html,img,img)),att)')], 2: [('images without html', (False, False, 3, 0), 'mixed(text,att,att,att)'), ('text and html', (True, True, 0, 0), 'alternative(text,html)'), ('text html and images', (True, True, 3, 0), 'alternative(text,related(html,img,img,img))'), ('html images and attachment', (False, True, 2, 1), 'mixed(related(html,img,img),att)'), ('text and attachments', (True, False, 0, 2), 'mixed(text,att,att)'), ('plain text only', (True, False, 0, 0), 'text'), ('everything', (True, True, 2, 2), 'mixed(alternative(text,related(html,img,img)),att,att)')], 3: [('images without html', (False, False, 4, 0), 'mixed(text,att,att,att,att)'), ('text and html', (True, True, 0, 0), 'alternative(text,html)'), ('text html and images', (True, True, 4, 0), 'alternative(text,related(html,img,img,img,img))'), ('html images and attachment', (False, True, 3, 1), 'mixed(related(html,img,img,img),att)'), ('text and attachments', (True, False, 0, 3), 'mixed(text,att,att,att)'), ('plain text only', (True, False, 0, 0), 'text'), ('everything', (True, True, 2, 3), 'mixed(alternative(text,related(html,img,img)),att,att,att)')], 4: [('images without html', (False, False, 5, 0), 'mixed(text,att,att,att,att,att)'), ('text and html', (True, True, 0, 0), 'alternative(text,html)'), ('text html and images', (True, True, 5, 0), 'alternative(text,related(html,img,img,img,img,img))'), ('html images and attachment', (False, True, 4, 1), 'mixed(related(html,img,img,img,img),att)'), ('text and attachments', (True, False, 0, 4), 'mixed(text,att,att,att,att)'), ('plain text only', (True, False, 0, 0), 'text'), ('everything', (True, True, 2, 4), 'mixed(alternative(text,related(html,img,img)),att,att,att,att)')], 5: [('images without html', (False, False, 6, 0), 'mixed(text,att,att,att,att,att,att)'), ('text and html', (True, True, 0, 0), 'alternative(text,html)'), ('text html and images', (True, True, 6, 0), 'alternative(text,related(html,img,img,img,img,img,img))'), ('html images and attachment', (False, True, 5, 1), 'mixed(related(html,img,img,img,img,img),att)'), ('text and attachments', (True, False, 0, 5), 'mixed(text,att,att,att,att,att)'), ('plain text only', (True, False, 0, 0), 'text'), ('everything', (True, True, 2, 5), 'mixed(alternative(text,related(html,img,img)),att,att,att,att,att)')]}
for _label, _args, _expected in _CASES[N]:
    check(_label, solve(*_args), _expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
images without html	`mixed(text,att,att)`	`mixed(text,att,att)`	Passed
text and html	`alternative(text,html)`	`alternative(text,html)`	Passed
text html and images	`alternative(text,related(html,img,img))`	`alternative(text,related(html,img,img))`	Passed
html images and attachment	`mixed(related(html,img),att)`	`mixed(related(html,img),att)`	Passed
text and attachments	`mixed(text,att)`	`mixed(text,att)`	Passed
plain text only	`text`	`text`	Passed
everything	`mixed(alternative(text,related(html,img,img)),att)`	`mixed(alternative(text,related(html,img,img)),att)`	Passed

SHA-256 / ec74f87d73b4fa1010c8151d39edf169ac8f01d74a67260bb62559e9e13dab15

Verification & scope

Stipulated offline model over pre-parsed MIME dictionaries; not a conforming MIME parser, generator or mail client. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:49:17.381581+00:00.

Case digest / f6214d5ea3b8ba16d29258806f5e11774dfff71c28a59ea1689c581c19a2d62a