How to protect a Plesk mail server against mail spoofing?

Question

• How to protect a Plesk mail server against mail spoofing?
• Others are sending emails through my Plesk mail server, how to stop this from happening?
• My Plesk mail server appears to be acting as an open mail relay and people are sending spam from it, what can be done to prevent this?

Answer

The first thing you should do is enable SPF check for incoming emails by following these steps:

1. Log into Plesk

2. Go to Tools & Settings > Mail Server Settings > SPF spam protection > Check the box to Enable SPF spam protection to check incoming mail

3. Set SPF checking mode to Reject mail if SPF does not resolve to “pass”

4. Scroll down and press Apply

Additionally, it is recommended to set up DKIM, SPF and DMARC as mentioned in the following article:

What is DKIM, SPF and DMARC protection?

If you are using the Plesk Email Security extension, you should also follow these steps:

1. Log into Plesk

2. Go to Tools & Settings > Plesk Email Security > Server Settings > Advanced

3. Under the Postfix - Strict Rules section, check the Enable strict rules box

4. Click Save

Additional information

How to protect a Plesk server from incoming spam and viruses?
DKIM, SPF, and DMARC Protection and ARC Support | Plesk Obsidian documentation