US Phone company mail servers are reporting email sent with MailKit contains bare CR about mimekit

[Saurbaum]

I'll see what I can dig out on Monday when I'm in the office.

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On Fri, 9 Feb 2024, 22:30 Jeffrey Stedfast, ***@***.***> wrote: Wrote up a quick unit test based on your protocol log to construct the exact same MimeMessage and then piped it through to a MemoryStream backed SmtpStream the same exact way that SmtpClient sends the message in the DATA command, but no luck reproducing (even without the Unix2Dos filter changes). I'm at a loss to reproduce this issue... — Reply to this email directly, view it on GitHub <#1004 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABXTQEBM6WZ3D4DKNNZQ3WLYS2PPTAVCNFSM6AAAAABDCAUQLWVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMYTSMZWGY4DQNRTHE> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[jstedfast]

Not sure if the above commit fixes this (sorta seems like it shouldn't?), but it's the only issue I could find.

[jstedfast]

Ok, so this is likely to either be a bug in MimeKit's Unix2DosFilter -or- MailKit's SmtpDataFilter.

Not sure which (if either) the bug exists in :-\

If it's not in either of those, not sure where it could be...

[jstedfast]

Would it be possible to attach the original text/plain and text/html content files? Those might help me diagnose this a bit.

[jstedfast]

Wrote up a quick unit test based on your protocol log to construct the exact same MimeMessage and then piped it through to a MemoryStream backed SmtpStream the same exact way that SmtpClient sends the message in the DATA command, but no luck reproducing (even without the Unix2Dos filter changes).

I'm at a loss to reproduce this issue...

[Saurbaum]

Welp this is utterly weird. Problem is definitely my end and not in [Mail/Mime]Kit.

If I inspect the strings in the debugger they are showing CRLF as expected. As soon as I dump them out to a file they revel their true colours.

[jstedfast]

But that still doesn't explain why carriers are saying your emails contain bare carriage returns right? Or am I confused?

[Saurbaum]

It seems I had in the HTML formatting some lines ending in LFCR. That seemingly would be processed into
LF
CR

And I think looking at the way it would convert the HTML into a plain text version it would end up with a series of LFCR at the start of the message which the viewer in Visual Studio was than trying to make human readable and not showing the actual data.

So the email message absolutely does have a bare CR in it because its companion LF is on the previous line. Making it harder to spot in my data was that when you have a chain of several together they look much more normal.
LF
CRLF
CRLF
CR