在读取邮件时 出现了邮件标题错误的问题

[cainiaosgh]

这是我在读取标题时出现的错误
Traceback (most recent call last):
File "C:\Users\石广慧\AppData\Local\Programs\Python\Python38\lib\site-packages\zmail\parser.py", line 150, in parse_headers
bname, bvalue = line.split(b':', 1)
ValueError: not enough values to unpack (expected 2, got 1)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "D:/pachong/基础知识/邮件发送zmail.py", line 33, in
mail1 = server.get_mails(1,mail[0])
File "C:\Users\石广慧\AppData\Local\Programs\Python\Python38\lib\site-packages\zmail\server.py", line 141, in get_mails
headers = self.get_headers(start_index, end_index)
File "C:\Users\石广慧\AppData\Local\Programs\Python\Python38\lib\site-packages\zmail\server.py", line 194, in get_headers
, headers, * = parse_headers(mail_header)
File "C:\Users\石广慧\AppData\Local\Programs\Python\Python38\lib\site-packages\zmail\parser.py", line 152, in parse_headers
raise ParseError('Invalid header:' + str(line))
zmail.exceptions.ParseError: Invalid header:b'dear guanghui'

上面的图片是我的邮件标题，请问这是什么原因？