Spasmodic rejections

[Andy]

(No, this is not a politics thread...) I am a member of a 6-person
committee which carries out its work by email. Occasionally, an email
from 'K' is rejected by my system; the log has no details on why. K is
on AOL; I'm on 1&1 and use TP. Rejection is perhaps one a fortnight, out
of 30-50 accepted.

I had previously set up a relay on my 1&1 account to copy all incoming
emails to my smartphone. K's rejected emails are copied. Also, they are
not dumped in my 1&1 spam folder. I conclude that it's TP doing the
rejecting.

I don't see any pattern in the addressees or content of the rejected
emails.

What, if anything, can I try next?

[Paul Wolff]

I was going to raise something rather similar, except that my ISP's mail
server does tell me that it can't deliver the email to TP. The root
cause is that the mail server is running delivery software (Courier)
which now implements RFC 6856 which is intended to permit UTF-8 more
generally in the mail headers.

Courier asks TP Connect if it will accept UTF-8, TP fails to give the
correct response, so the message isn't sent to TP. In your case, your
smartphone presumably does give the correct response, so does get the
email.

Courier does send TP this message, without admitting that it's generated
internally:

=======
This E-mail message was determined to be Unicode-formatted but
your E-mail reader does not support Unicode E-mail.

Please use an E-mail reader that supports POP3 with UTF-8 (see
https://tools.ietf.org/html/rfc6856.html).

This can also happen when the sender's E-mail program does not
correctly format the sent message.

The original message is included as a separate attachment so
that it can be downloaded manually.
=======

It then attaches a file with a .dat extension, which for a long time
caused me to delete the messages as malware. But they seem to be just
raw text in which the original email can be found unformatted.

If you read the RFC linked to above, see Section 7 especially.

Paul

Post by Andy
(No, this is not a politics thread...) I am a member of a 6-person
committee which carries out its work by email. Occasionally, an email
from 'K' is rejected by my system; the log has no details on why. K is
on AOL; I'm on 1&1 and use TP. Rejection is perhaps one a fortnight,
out of 30-50 accepted.
I had previously set up a relay on my 1&1 account to copy all incoming
emails to my smartphone. K's rejected emails are copied. Also, they
are not dumped in my 1&1 spam folder. I conclude that it's TP doing
the rejecting.
I don't see any pattern in the addressees or content of the rejected
emails.
What, if anything, can I try next?