webmail sometimes will stop loading until all IPs for that user are released

Problem reported by Rami El-Zein - 6/19/2026 at 3:08 AM

Submitted

Screenshot 2026-06-19 at 10.21.31.pngScreenshot 2026-06-19 at 10.21.21.png

Hello,

My server is hosted on AWS and runs SmarterMail on Linux. The server specifications are:

32 CPU cores
64 GB RAM
14 TB SSD storage

On a typical day, the load average stays between 1.5 and 2.0, with approximately 800 concurrent user connections consisting of:

~200 Webmail connections
~500 SMTP connections
A few POP connections
~100–150 MAPI/EWS connections

As a maintenance measure, I restart the SmarterMail service every Sunday night because I notice that swap space gradually decreases over time, although it never drops below 6 GB.

My current connection limits are configured as follows:

IMAP: 5,000 maximum connections
XMPP: 300 maximum connections
POP: 500 maximum connections

The issue I'm experiencing is that I occasionally receive support calls from clients reporting that they cannot access Webmail, and IMAP access also stops working for them. When I log into Webmail using the affected user's account, the Inbox keeps spinning and never loads, as shown in the attached screenshots.

The only way I have found to resolve the issue is to manually drop that user's active connections, after which Webmail and IMAP immediately start working again.

I have attached screenshots for reference. Has anyone encountered a similar issue or have any suggestions on what could be causing this and how to prevent it?

Thank you.

2 Replies

Reply to Thread

Douglas Foster Replied

6/19/2026 at 4:23 AM

Is there a firewall involved? I am wondering if a NAT exhaustion has occurred.

Rami El-Zein Replied

6/19/2026 at 5:09 AM

Hello Douglas, thanks for the suggestion.

To my knowledge, this is a fairly standard SmarterMail deployment on a single AWS instance. There is no external firewall appliance, load balancer, or NAT device in front of the server other than the standard AWS networking components.

What makes me think it may not be NAT exhaustion is that the issue appears to affect individual users rather than the entire server. When it happens, the affected user's Webmail Inbox keeps loading indefinitely and IMAP access also stops working for that user. As soon as I drop that user's active connections, everything immediately starts working again.

Would NAT exhaustion typically present itself on a per-user basis like this, or would it be more likely to impact all users and services simultaneously?

Back to Community Threads

Please leave this box unchecked

Reply to Thread

Enter the verification text