IreneMcBeatle

Thanks. I couldn’t find out about Qmail. I’ve tested patches but they didn’t help.

Finally I replaced files class-phpmailer and class-smtp with previous versions (5.2.1) and the mail started working again.

I hope that the next WordPress update will resolve this issue.

If you mean hosting provider, they don’t have filters.

I also have problems with e-mail after update to 3.6.1. Here is my topic with details: https://www.ads-software.com/support/topic/mail-not-working-after-upgrade-to-361