<![CDATA[Port 25 inbound connection timeout and missing email]]>Can heavy CPU usage during peak load times cause problems with email reception, to the point where emails are “not handled” because port 25 is unreachable from outside the network, bringing to “25: Connection timed out” and to Undelivered Mail Returned to Sender.

I'm asking this question because I've had a similar problem and I'd like to know how to mitigate it.

I've already limited maximum CPU usage to 80% of every single app hosted on Cloudron, but I'd like to understand how the overall load is being managed, to the point where 25 port stops responding.

No any log on Cloudron (Server, Mail) about ”not handled” email.

Edit: allocated Ram show that every app and service has enough Ram. My question also is: there is a way to assign maximum CPU usage to each service, to “keep alive” essential one?

Edit2: Peak was caused from an high number of web pages served and a lot of incoming email received in very short time, like a time frame of 10-15 minutes.

Thanks a lot

]]>https://forum.cloudron.io/topic/15303/port-25-inbound-connection-timeout-and-missing-emailRSS for NodeSat, 11 Jul 2026 20:59:53 GMTThu, 26 Mar 2026 16:26:17 GMT60<![CDATA[Reply to Port 25 inbound connection timeout and missing email on Wed, 15 Apr 2026 16:36:23 GMT]]>@james Yes, this is a great find. Thanks a lot for your cooperation.

In email service’s logs no any log...

Whenever you want, I can reproduce issue and I can send you raw log.

Keep me posted.

]]>https://forum.cloudron.io/post/123484https://forum.cloudron.io/post/123484Wed, 15 Apr 2026 16:36:23 GMT<![CDATA[Reply to Port 25 inbound connection timeout and missing email on Wed, 15 Apr 2026 10:01:39 GMT]]>Hello @p44
That is an interesting find.
Could save the logs of the mail service when it was failing somewhere so we can request it later from you?

]]>https://forum.cloudron.io/post/123446https://forum.cloudron.io/post/123446Wed, 15 Apr 2026 10:01:39 GMT<![CDATA[Reply to Port 25 inbound connection timeout and missing email on Wed, 15 Apr 2026 05:35:43 GMT]]>Thanks again @james for your cooperation.

I can confirm that after removing custom Spamassassin rules from Email > Settings > Spam Filtering > Custom Spamassassin rules problem has been solved.

However, further testing would be needed to determine which rules interacted negatively with emails, potentially causing false positives.

]]>https://forum.cloudron.io/post/123431https://forum.cloudron.io/post/123431Wed, 15 Apr 2026 05:35:43 GMT<![CDATA[Reply to Port 25 inbound connection timeout and missing email on Fri, 10 Apr 2026 20:06:55 GMT]]>Ok @james. I’ll do more accurate research

]]>https://forum.cloudron.io/post/123173https://forum.cloudron.io/post/123173Fri, 10 Apr 2026 20:06:55 GMT<![CDATA[Reply to Port 25 inbound connection timeout and missing email on Fri, 10 Apr 2026 18:34:32 GMT]]>Hello @p44
A momentary view of the IOPS might not be good enough to evaluate this.
Since you mentioned when the system is under high load the issue is present, you should observe / log the IOPS while the system is under load.

]]>https://forum.cloudron.io/post/123168https://forum.cloudron.io/post/123168Fri, 10 Apr 2026 18:34:32 GMT<![CDATA[Reply to Port 25 inbound connection timeout and missing email on Fri, 10 Apr 2026 17:06:20 GMT]]>@james Thanks a lot for your question.

IOPS it seems to be good...

Block Size | 4k            (IOPS) | 64k           (IOPS)
  ------   | ---            ----  | ----           ---- 
Read       | 510.82 MB/s (127.7k) | 870.43 MB/s  (13.6k)
Write      | 512.17 MB/s (128.0k) | 875.01 MB/s  (13.6k)
Total      | 1.02 GB/s   (255.7k) | 1.74 GB/s    (27.2k)
           |                      |                     
Block Size | 512k          (IOPS) | 1m            (IOPS)
  ------   | ---            ----  | ----           ---- 
Read       | 595.93 MB/s   (1.1k) | 1.49 GB/s     (1.4k)
Write      | 627.60 MB/s   (1.2k) | 1.59 GB/s     (1.5k)
Total      | 1.22 GB/s     (2.3k) | 3.09 GB/s     (3.0k)
]]>https://forum.cloudron.io/post/123163https://forum.cloudron.io/post/123163Fri, 10 Apr 2026 17:06:20 GMT<![CDATA[Reply to Port 25 inbound connection timeout and missing email on Fri, 10 Apr 2026 14:04:37 GMT]]>Hello @p44
Have you looked into the the IOPS stats?

]]>https://forum.cloudron.io/post/123156https://forum.cloudron.io/post/123156Fri, 10 Apr 2026 14:04:37 GMT<![CDATA[Reply to Port 25 inbound connection timeout and missing email on Fri, 10 Apr 2026 11:56:50 GMT]]>Hi @james I’m still managing this problem. There is a way to manage Haraka timeout to avoid this Connection timed out issue, eg. making longer timeout?

]]>https://forum.cloudron.io/post/123153https://forum.cloudron.io/post/123153Fri, 10 Apr 2026 11:56:50 GMT<![CDATA[Reply to Port 25 inbound connection timeout and missing email on Fri, 27 Mar 2026 14:50:43 GMT]]>@james Thanks a lot, I didn’t have any crash of Mail service and also RAM is ok. I’ll take a proper look to IOPS. Thanks for your advices.

]]>https://forum.cloudron.io/post/122588https://forum.cloudron.io/post/122588Fri, 27 Mar 2026 14:50:43 GMT<![CDATA[Reply to Port 25 inbound connection timeout and missing email on Fri, 27 Mar 2026 13:31:24 GMT]]>Hello @p44

I would assume this is not only a CPU/RAM issue but also an IOPS issue.
A very high system load can also occur without the CPU and RAM being used too much.
In this case it is almost always the IOPS. So the system storage can't keep up.
Depending on your server setup and provider this might be worth looking into if your server is using HDD, SSD, NVMe drives or a shared storage from the provider.
We had multiple reports of vServers showing this load / IOPS behaviour when there were underlying issues with the whole provider node.
One time it was a netcup node failing RAID system that caused all vServers on that node to have massive IOPS and load issues.
Which was also first denied by the first level support and only after providing detailed performance measurements they acknowledged that something must be wrong with their storage raid.

Port 25 not being inaccessible could also hint towards the mail service crashing or running out of memory.
Please check your mail service in Cloudron if you might need to increase the RAM and also check the logs of the mail service for crash reports.

]]>https://forum.cloudron.io/post/122585https://forum.cloudron.io/post/122585Fri, 27 Mar 2026 13:31:24 GMT