Unable to send mails using nullmailer installed on the same machine as Stalwart

[mediocretwo]

Hi, I'm new to self hosting my email server, and I'm trying to send emails using nullmailer on my server, to forward them to Stalwart running in a docker container on the same machine. The idea is, I want to send emails using nullmailer (from my own domain) to my protonmail email account through Stalwart, regarding the status of my server. Nullmailer is able to reach Stalwart on the network, but the email from Nullmailer is getting rejected at SMTP EHLO stage in Stalwart. The logs show the following message: INFO session{instance="smtp" protocol=Smtp remote.ip="172.30.0.1" remote.port=51446}: smtp::inbound::ehlo: context="ehlo" event="reject" reason="invalid" domain="jmserver". I'm pretty lost on whats happening here, would really appreciate some help. Thanks!

[mdecimus]

Hi,

This is because your client is not using a fully-qualified domain name in the EHLO command. This behaviour is usually associated with spammers so it is disabled by default. You can disable this security feature from the configuration file but it is not recommended.

[mediocretwo]

I have tried turning off the 'reject non-FQDN' setting and this time there is nothing happening in stalwart. Literally there is no log message about what happened to the test email I sent from my system. The nullmailer program reported that the mail failed to deliver though.

[mdecimus]

Try setting the debug level to trace and check the Stalwart logs.