Help: OVH blocked port 25 for a month. What I can do to have working emails on another port

[nabuhonodozor]

Dear All,
I have quite serious issue.
My server provider blocked port 25 for my server bacause of spam. One of my client have main account email set to catch all and spammers start to bounce mails. Even Ive set hourly email rate limit for a domains to 500 this was easly bypassed. Now Ive changed this so mails are discarded but the main problem is that OVH blocked port 25 for a month. Its a serious issue for me as I have many clients on this server.

Can You help me with this - can I force cPanel/Exim to use different port than 25?

I am looking forward to some hints/ ideas.

Kind regards,
Piotr

 

[Infopro]

The docs should be helpful:
Service Manager - cPanel Documentation

exim on another port You can allow users to run Exim on an additional port. (Exim will also run on the default port, 25.)
Remember: In the text box, specify the additional port number on which you would like to allow Exim to run.

 

[nabuhonodozor]

The docs should be helpful:
Service Manager - cPanel Documentation

Thank You for tip.
I have configured additional 587 many years ago. Some mails pass through the mail server but some of them are stuck in sending que. Opening them I can see that they

-interface_address 127.0.0.1.25

.
I dont know how to force all outgoing mails to 587.

 

[nabuhonodozor]

As for now OVH support was kind enough to remove port block.

In the future - from the lack of responces to this question, I assume theres no way to use cPanel without fully working port 25.

Please close the thread.

 

[JaredR.]

There is no way to host mail on a server without a fully working port 25.

There is a misconception that we sometimes see about ports 25 and 587. Port 587 is the mail submission port. It is the port that end users are supposed to use to send mail to a server for relaying. The server then connects to the destination server on port 25 to actually send the mail to where it belongs.

There is no way to bypass this. In support, we sometimes get inquiries from customers who want to change the SMTP port from 25 to 587, because they think it will prevent spam (the idea being, if the spammers do not know the SMTP port, they will not be able to send their spam). This is simply does not work. Port 25 is the Internet standard for sending mail, so if you do change your SMTP port from 25 to 587, servers that try to send mail to your server will only see that they cannot connect to port 25, and they will not try port 587, because that is not what port 587 is for.

Port 587 is for incoming mail that your customers want to send through your server. It is not for outgoing mail, or for one server sending mail to another. Note that Exim listens on port 587 by default, no custom configuration needed, so your customers can connect to send their mail through your server.

In short, if port 25 was blocked, there is a reason, and you need to work with the hosting provider to find the reason and fix the underlying cause. Trying to change to another port for either incoming or outgoing mail is just not going to work. This is not a cPanel limitation. It is just the way Internet mail works.

 

[nabuhonodozor]

Thank You cPanelJared for detailed explanation. In the last days I was under attack from hackers to that extend that few times server restarted just because of excessive traffic.
What I see it that the times for small hosting companies is quickly come to and end - simply You cant compete with thousands of zombies grandma PC's attacking it every nanosecond. I need to find a solution to distribute mail servers across few mashines forming a cluster with different IP etc.

Again - thank You cPanelJared!

 

[JaredR.]

You really should not need rotate outbound IP addresses for outgoing mail, even on a busy server. If port 25 was blocked, the usual reason is that the data center either detected, or received complaints about, mail that is perceived to be spam. Trying to change the SMTP port or trying to rotate outgoing IP addresses really addresses the symptom, not the problem. The best way to approach this is to examine the mail usage of your customers and suspend or terminate accounts that are sending mail that may be perceived as spam.

Without addressing the underlying problem, rotating IP addresses for outgoing mail is a way to get several IP addresses, instead of just one, blocked or listed in a blacklist.

Sometimes scripts that your customers use on their sites may be exploited to send spam, without your customer even knowing it. Suspending a site with scripts that are being exploited to send spam, is a way to get your customer's attention and also prevent more spam from being sent while the site scripts are being updated/patched/replaced.

 

[JaredR.]

I wanted to also mention that you can now enable SpamAssassin on outgoing mail as well as incoming. This will increase the server load (how much will depend on how much mail is being sent) but it could help to avoid having the server send out mail that is considered spam.