SMTP starttls certificate error

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1

I’m pretty sure I’m missing something obvious here.. but I’ve got vaultwarden set up using an SSL certificate (not self signed) using Caddy - Web Vault is working fine, but I’m having trouble getting SMTP work unless I turn off starttls.

Whenever I try to send a test message I get the following: SMTP error: Connection error: Connection error: error: 0A000086:SSL routines:tls_post_process_server_certificate:certificate verify failed:…/ssl/statem/statem_clnt.c:1889: (self-signed certificate)

I’m guessing the problem is the SMTP connection is trying to use a self signed certificate rather than my actual one? Again, I can make it work if I turn off Secure SMTP - which honestly is probably OK in my case as my SMTP server is on my local network.. but I feel like I am missing something obvious here.

Can anyone offer any suggestions or point out what I am doing wrong here?

2

A little update here in case anyone else runs into this. The problem is apparently NOT vaultwarden at all, but the SSL certificate assigned the receive connector on my Exchange server.

I found some information here about how to assign a certificate to individual connectors, and now vaultwarden is able to send email using starttls: