Delivery of mail to multiple "to" addresses when one address is invalid

[heikkiorsila]

Server A is using msmtp for mail forwarding to another server B where postfix relays the mail forward. The postfix is configured to reject emails with some criteria, e.g.:

smtpd_recipient_restrictions =
       reject_non_fqdn_recipient,
       reject_unknown_recipient_domain,
       check_recipient_access hash:/etc/postfix/recipient_access

If server A sends email with multiple "To" addresses but one of them does not pass the checks at postfix on server B, then none of the "To" address will receive email. At least the valid email addresses should get delivered. Is there an option that we can use to send email separately to "To" specified addresses or handle this in other way? Please advice how to fix this..

Normally, we would try to avoid sending email to bad addresses, but this is a customer system where they may enter bad email addresses (accidently).

[marlam]

There is no builtin option to "split" a mail and send for each recipient individually.
But you could implement this with a script that handles the mail before msmtp does: read the mail, extract all recipients, call msmtp for each recipient individually, passing the recipient on the command line and avoiding -t/--read-recipients.

[heikkiorsila]

Thanks for a quick reply, Martin! Is it possible to receive feedback from msmtp about which email addresses where rejected or which were valid if we send to multiple addresses at once?

[marlam]

Msmtp prints information about where in the SMTP session an error occurred, and what the error message given by the SMTP server was.

So I would expect a message like recipient address %s not accepted by server: <MESSAGE-FROM-SERVER>.

However, what you get depends on the SMTP server. It may chose to reject the mail only after all RCPT TO commands have been accepted, and then just give a generic error code and no detailed message.

Postfix typically gives you detailed information.