Send urgent/high priority e-mails automatically

Question

Although using Python, I set the headers as described here would result in flagging my e-mails as spam by SpamAssassin.

I am sending reminders for un-paid invoices, so I would like to do anything in my power to make the receiver aware of the e-mail - but this cannot happen if my e-mail ends up in the spam folder due to the urgent flag.

Using the X-MSMail-Priority in the header would add a positive spam score from MISSING_MIMEOLE, using X-Priority would add a positive score. Only using Priority in the header are not implemented in Thunderbird Mail client nor in RoundCube webinterface, thus the urgency is not shown.

What can I do to make my e-mails urgent, but simultaneously make SpamAssassin (and other filters) happy?

Answer 1

You cannot control how others filter their spam. If you find that anything in your mail triggers common spam filters, you have to remove that if it is important that your users get those emails. The priority header is abused by spammers, so you cannot use that.

Likewise, I would expect any other unauthenticated priority indicator to be abused by spammers, so there won’t be any way. Possibly signing these headers using DKIM and deploying DMARC (with a strict policy) on your domain might help, but I do not know for sure that filters such as spamassassin are smart enough to consider the priority header authenticated in such cases.

Deploying DMARC might be a good idea anyways for transactional mail, to prevent spoofing.