使用Python imaplib下载的PDF邮件附件无法打开的问题求助

使用Python的imaplib库下载指定邮件中的PDF附件，代码执行后文件已按预期下载，但所有PDF均无法正常使用：Zathura、Google Chrome无法打开，PdfReader模块也无法识别，且文件体积大于正常大小。

代码示例 #

import imaplib
import base64
import os
import email

user = 'my email'
passwd = 'my password'
directory = 'directory I want my downloaded files to go to'

mail = imaplib.IMAP4_SSL('imap.gmail.com')
mail.login(user, passwd)
mail.select('INBOX')

res, data = mail.search(None, 'FROM "email I want to download attachments from" SUBJECT "subject I want"')
mail_ids = data[0]
id_list = mail_ids.split()

for num in data[0].split():
    res, data = mail.fetch(num, '(RFC822)')
    raw_email = data[0][1]
    raw_email_string = raw_email.decode('utf-8')
    email_message = email.message_from_string(raw_email_string)

    for part in email_message.walk():
        if part.get_content_maintype() == 'multipart':
            continue
        if part.get('Content-Disposition') is None:
            continue
        fileName = part.get_filename()
        
        if bool(fileName):
            filePath = os.path.join(directory, fileName)

            if not os.path.isfile(filePath):
                fp = open(filePath, 'wb')
                fp.write(part.get_payload(decode=True))
                fp.close()

错误提示 #

Zathura打开时终端输出：

error: cannot recognize version marker
warning: trying to repair broken xref
warning: repairing PDF document
warning: name is too long
warning: ...repeated 1376 times...
error: no objects found
error: could not open document

Chrome打开时提示：

Error
Failed to load PDF document.

问题原因 #

核心问题是错误地将二进制格式的原始邮件内容解码为UTF-8字符串，再用email.message_from_string()解析。邮件的RFC822内容本身是二进制结构，解码为UTF-8会破坏附件的二进制数据（比如PDF的字节流），导致保存的文件损坏。

修复步骤 #

1. 跳过UTF-8解码步骤，直接用email.message_from_bytes()解析原始二进制邮件内容。
2. 保留二进制模式写入文件的逻辑（代码中已实现，无需修改）。

修改后的代码 #

import imaplib
import os
import email

user = 'my email'
passwd = 'my password'
directory = 'directory I want my downloaded files to go to'

mail = imaplib.IMAP4_SSL('imap.gmail.com')
mail.login(user, passwd)
mail.select('INBOX')

# 替换转义双引号为普通双引号，提升可读性
res, data = mail.search(None, 'FROM "email I want to download attachments from" SUBJECT "subject I want"')
mail_ids = data[0]
id_list = mail_ids.split()

for num in mail_ids.split():
    res, data = mail.fetch(num, '(RFC822)')
    raw_email = data[0][1]
    # 直接解析二进制邮件内容，避免编码破坏
    email_message = email.message_from_bytes(raw_email)

    for part in email_message.walk():
        if part.get_content_maintype() == 'multipart':
            continue
        if part.get('Content-Disposition') is None:
            continue
        fileName = part.get_filename()
        
        if fileName:
            filePath = os.path.join(directory, fileName)

            if not os.path.isfile(filePath):
                # 使用with语句自动管理文件句柄，避免资源泄漏
                with open(filePath, 'wb') as fp:
                    fp.write(part.get_payload(decode=True))

额外优化点 #

• 用with语句替代手动调用open()和close()，更安全且代码更简洁。
• 将搜索条件中的"替换为普通双引号，提升代码可读性。

内容的提问来源于stack exchange，提问作者Nickylp