Limit NAT VPS Email Delivery

Wira_Soenaryo

Hai..

Currently I have one dedi server put on colocation.
I install virtualizor under Ubuntu 20.04.

Because I only have limited IP Address, I plan to create NAT VPS for some of my client. May I know how to prevent / limit email out from each NAT VPS? What I mean is, because NAT VPS share a same IP Address, I'm afraid if one VPS got hacked and sent a lot of SPAM email... then the IP being blacklisted, will sacrifice whole client on that particular IP Address.

Any suggestions are very welcome.
Thanks...

lorian

As MTAs normally use port 25/tcp to send emails, it is as easy as just block this port outbound. e.g. ufw deny out 25

kdh

Block commonly used SMTP ports e.g: 25, 465, 587, and 2525.

Wira_Soenaryo

Thank you for the suggestion. Then it will totally block the NAT VPS from sending out an email... Any other way instead of fully block, but limit the number of email out?

arda

Limited spam is still spam. If I was stuck with NAT VPS, I'd consider using a 3rd party SMTP service.

lorian

@kdh said:
Block commonly used SMTP ports e.g: 25, 465, 587, and 2525.

I would not block 587, as it is only used by mailclients and therefore would only block 3rd party mailservices.

yoursunny

@lorian said:
As MTAs normally use port 25/tcp to send emails, it is as easy as just block this port outbound. e.g. ufw deny out 25

sudo ufw route deny out on uplink to any port 25