Email accounts suddenly not sending emails after upgrade to Sentora 2.x.x

[TGates]

I’m pretty new to managing a server with Sentora, so please excuse me if this is something simple that I missed.
I recently upgraded my panel to version 2.x.x and everything seemed to go smoothly at first. The control panel loads fine, domains are still listed, and my email accounts are all still there. However, since the upgrade, I’ve noticed that none of my email accounts can send outgoing emails anymore.
Incoming emails still arrive without any problem, but when I try to send a message from webmail or an email client (like Thunderbird), it either times out or shows an SMTP error.
Here are a few things I already checked:

• Restarted the server and mail services
  
• Verified that ports 25 and 587 are open
  
• Checked that the email accounts are still active in the panel
  

I’m wondering if something changed in the mail configuration after the upgrade that I might need to update manually.
Has anyone else experienced this after updating to Sentora 2.x.x? Any suggestions on what logs or settings I should check first?

I haven't heard of this issue yet. I'll look into it.

What is the smtp error? Wrong password? connection issue? What do your mail logs show?