Content type key header added by iOS mail app contains ‘@yahoo.com’, - causing mail to get rejected by some IMAP servers.

[uandme72]

Content type key header added by iOS mail app contains ‘@yahoo.com’, - causing mail to get rejected by some IMAP servers.
Issue is occurring on all iOS versions including 14.6.
On the iPhone, I am unable to forward a mail containing attachments received from a web browser based @yahoo.com or @icloud.com mail account.
When the iPhone native mail app forwards a mail received from @yahoo.com or @icloud.com mail account using a web browser like Safari, it adds the following header content to the mail:
Header added by iPhone mail app:

********

--Apple-Mail-91EF9D82-D8B5-41DD-A98A-69489ED47254
Content-Type: image/jpeg;
name=image0.jpeg;
x-apple-part-url="xxxx-yyyy-zzzz@yahoo.com"
Content-Disposition: inline;
filename=image0.jpeg
Content-Transfer-Encoding: base64
Content-Id: xxxx-yyyy-zzzz[AT]yahoo.com

The header added by iPhone mail app is rejected by some third party IMAP mail accounts who reject the message from iOS mail app. The error message generated at IMAP mail servers is as follows:
Mail send failure log:

*********
Action: failed
Status: 5.0.0 (permanent failure)
Remote-MTA: dns; [xxx.xxx.xxx.xxx]
Diagnostic-Code: smtp; 5.3.0 - Other mail system problem 550-'5.7.1 Attachment type not allowed. File "image0.jpeg; x-apple-part-url="xxxxxxx-yyyyy[AT]yahoo.com" has the unacceptable extension "com"' (delivery attempts: 0)

**Is the error of mail rejection on account of iPhone incorrectly adding the header, or is the mail server behaving incorrectly by wrongly rejecting the mail?**

 

[jsamuelson]

This must be part of Apple's effort to lock down Mail; if you haven't already can you file a report with Apple?

Often mail servers will reject any file with an executable extension. Usually this is a .exe, .bat etc type but I could see why .com would be rejected too as it's a DOS executable.

I suspect this can be fixed by placing the email being used as an identifier (Content-Id) before the attachment filename in the header, so this is probably a bug on Apple's side.

 

[uandme72]

This must be part of Apple's effort to lock down Mail; if you haven't already can you file a report with Apple?

Often mail servers will reject any file with an executable extension. Usually this is a .exe, .bat etc type but I could see why .com would be rejected too as it's a DOS executable.

I suspect this can be fixed by placing the email being used as an identifier (Content-Id) before the attachment filename in the header, so this is probably a bug on Apple's side.

I have reported it to Apple.
So far no resolution after 2 months.