使用Python imaplib从Outlook取邮件时无报错但部分邮件无法获取

现象说明 #

使用Python的imaplib从Outlook收件箱拉取邮件，多数情况运行正常，但偶尔出现异常：服务器返回OK结果、目标UID有效且收件箱中可见该邮件，却无法获取邮件数据。这类问题邮件多为回复邮件，主体字符数约5k-10k，部分包含特殊字符，多数带有大量文本页脚，收件人/抄送人约5人。最特殊的是服务器不返回BAD或其他错误信息，仅返回OK但无数据返回。

已执行的排查操作 #

• 确认邮件存在：通过UID搜索能找到目标邮件，且收件箱中可见
• 尝试多种FETCH命令：(BODY.PEEK[HEADER.FIELDS (SUBJECT)])、RFC822.HEADER、FLAGS
• 将问题邮件导出为msg文件，检查格式未发现异常

脚本基础设置 #

import imaplib  # 已修改_MAXLINE = 50000000
server = imaplib.IMAP4_SSL(imap_server, imap_port)  
result, data = server.uid('FETCH', 42859, '(BODY.PEEK[HEADER.FIELDS (SUBJECT)])')

相关测试日志 #

UID搜索结果（范围42858-42865） #

10:35.18 > b'FOFI4 EXAMINE INBOX'
  10:35.47 < b'* 11892 EXISTS'
  10:35.47 < b'* 11892 RECENT'
  10:35.47 < b'* FLAGS (\\Seen \\Answered \\Flagged \\Deleted \\Draft $MDNSent)'
  10:35.47 < b'* OK [PERMANENTFLAGS ()] Permanent flags'
  10:35.47 < b'* OK [UNSEEN 3] Is the first unseen message'
  10:35.47 < b'* OK [UIDVALIDITY 14] UIDVALIDITY value'
  10:35.47 < b'* OK [UIDNEXT 43441] The next unique identifier value'
  10:35.47 < b'FOFI4 OK [READ-ONLY] EXAMINE completed.'
  10:35.47 > b'FOFI5 UID SEARCH (UID 42858:42865)'
  10:35.51 < b'* SEARCH 42859 42862 42865'
  10:35.51 < b'FOFI5 OK SEARCH completed.'

可见问题邮件UID 42862在搜索结果中存在。

正常邮件（UID 42859）的FETCH结果 #

10:38.79 > b'FOFI6 UID FETCH 42859 (BODY.PEEK[HEADER.FIELDS (SUBJECT)])'
  10:38.87 < b'* 11726 FETCH (BODY[HEADER.FIELDS (SUBJECT)] {126}'
  10:38.87 read literal size 126
  10:38.87 < b' UID 42859)'
  10:38.95 < b'FOFI6 OK FETCH completed.'
---
result: OK
data:   [(b'11726 (BODY[HEADER.FIELDS (SUBJECT)] {126}', b'Subject: XXX'), b' UID 42859)']

问题邮件（UID 42862）的FETCH结果 #

16:07.86 > b'OLDP6 UID FETCH 42862 (BODY.PEEK[HEADER.FIELDS (SUBJECT)])'
  16:09.08 < b'OLDP6 OK FETCH completed.'
---
result: OK
data:   [None]

问题邮件的RFC822.SIZE查询结果 #

11:35.69 > b'MOMM6 UID FETCH 42862 (RFC822.SIZE)'
  11:35.72 < b'* 11727 FETCH (RFC822.SIZE 120380 UID 42862)'
  11:35.80 < b'MOMM6 OK FETCH completed.'
---
result: OK
data: [b'11727 (RFC822.SIZE 120380 UID 42862)']

邮件大小与正常邮件相比无异常。

问题邮件的FLAGS查询结果 #

08:50.93 > b'MFBH6 UID FETCH 42862 (FLAGS)'
  08:50.96 < b'* 11727 FETCH (FLAGS (\\Recent) UID 42862)'
  08:51.04 < b'MFBH6 OK FETCH completed.'
---
result: OK
data: [b'11727 (FLAGS (\\Recent) UID 42862)']

求助需求 #

已检查问题邮件的属性和格式，未发现共性特征，也未找到相关技术文档或案例说明该现象。希望了解可尝试的其他排查命令或方向。

内容的提问来源于stack exchange，提问作者Amy