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I have recently by chance found out, that some specific emails sent via msmtp simply do not arrive.
Most emails go through, but some, that follow some specific, very strange rules, are lost.
The command always successfully terminates, the verbose output is nearly identical.
I don't want to post it here because I don't know which portions are security relevant.
What differs is:
(sometimes) a single digit in the subdomain of the mailserver that is connected to
The line '<-- 250-XLOOP some_long_id^M' appearing twice
obvious stuff such as date and changed subject
I am only able to reproduce this with the mail address respiranto@icloud.com, for which respiranto is the authentication name.
An example email that does not arrive (it is sent by calling `msmtp -t < email_file'):
To: <respiranto@icloud.com>
From: respiranto@icloud.com
Subject: respiranto abc
Subject: boring
Sender:What has no effect, i.e. the email is lost:
Replacing 'abc' by any string consisting entirely of lower case characters of the english alphabet or by colon-separated list where one of its elements which is not the first one must be either 'boring' or 'p'
In the first 'Subject:' line, 'respiranto' can get appended '.xy' where xy is a short string, preferably of 2 or 3 characters, though not all work.
Right after 'Sender:' (in the same line), one can, after a space char, add an alphabetic string optionally followed by an @ sign and a not regulated string.
In the line after 'Sender:', one can add any string with a length less or equal to 8.
If the 'Sender:' line and the following are left unmodified', the subsequent lines can be filled with anything, though this seems not to work always.
Adding a short string before and/or after 'boring' in the second 'Subject:' line, separated by a non-alphanumeric character, e.g. 'Subject: 2a+ boring?_T'
Appending precisely '<something>' right after 'respiranto' in the first 'Subject:' line. - E.g. '<somethink>' does not work.
What has an effect, i.e. the email arrives:
Decapitalizing 'To' or the first occurence of 'Subject'.
Changing the word 'boring' to anything else, except by capitalizing individual characters.
I certainly have not caught all the scenarios, though this should be sufficient to get confused.
I assume, that the problem is somehow, that the later lines are interpreted as part of the header, which causes a problem under certain conditions.
Though, I don't know, whether the problem is at msmtp's side or at the mailserver's side.
Does anyone have an idea what could be the cause for this?
And can anyone confirm this strange behaviour?
EDIT:
I am unable to reproduce this with other smtp clients, such as icedove, mutt or ssmtp, though this might be related to the fact, that those do a little more formatting on their own.
Last edited by respiranto (2016-01-02 23:58:56)
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