I think that the mail from NS (see attachment, no spam, this is clean mail) triggers some errors in secpoint and it is not delivered to the mailserver.
It's not a sql injection. The mail subject contains a 0A (line feed) at the beginning, which causes the problem:
The line feed causes the Subject be written to a new line in the qf file
And when sendmail tries to analyze the qf file to deliver the message, it cannot handle it and throws the error.
If the subject starts with a newline (0A) which isn’t correctly handled by sendmail, isn’t it a option to remove the newline? (And/or strip all forbidden characters from the subject line)
Why is this not a problem if the not delivered message is released from the archiver?
Modifying sendmail is not the best option. The best thing to do is submit
the problem to the sendmail developers. Before that, we may also try and
update sendmail to the latest version.
The message is delivered correctly from the mail archiver because it
doesn't rely on the qf file, which is deleted once the message has been
stored to the mail archiver and delivered to the recipient.