By way of update, it now appears that my iOS WireGuard client is connecting successfully, so I have re-enabled the firewall rule on the host that permits ports 587 and 993 to be reached only over the WireGuard interface. I plan to continue testing the reliability of the connection.

As an aside, I have found the kernel-based Linux WireGuard implementation to be highly reliable.

On 4/7/23 17:58, Jason White via luv-main wrote:
Dear Linux users,

I run a small server that provides e-mail, among other services. For this purpse, it runs Postfix and Dovecot - there's nothing surprising about it.

Are there any additional measures that I should take these days to secure it, especially against authentication-related attacks?

I believe the passwords are reasonably strong and unique (i.e., they aren't used for any other services). Also, fail2ban is running, and blocking hosts that fail to authenticate too often. Of course, only TLS connections are permitted, except on port 25. That is, StartTLS is mandatory.

I tried making ports 587 and 993 available only via a WireGuard connection. This worked well, except for an Apple iOS client that, unfortunately, lost Internet access entirely whenever I attempted to enable the WireGuard configuration. This configuration had previously worked, so a regression was introduced at some point, and others have apparently run into similar issues with iOS 16. Also, I've left certain other services, including ssh, available only via the WireGuard connection, despite having opened 587 and 993 for now.

For more general mail security, I have configured SPF, DKIM, DMARC and DANE. I'm using Rspamd for spam filtering, and I subscribed to the Spamhaus Data Query Service, which reduces incoming spam considerably. (I'm below the threshold at which they charge for the service.)

Is there anything else that I should be doing on the security front?


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