Does anyone know how to ban an IP from using SMTP via the hosts.deny file? I thought it was:
SMTP: 123.456.789.123
but that didn't seem to do anything. I did a quick search on Google but didn't turn up anything in the first couple of pages.

Note: I'm not trying to ban a spammer, this is a long-time customer who for some reason has started connecting to the SMTP server several times a second and it's causing problems. I don't want to list their IP under ALL: in the hosts deny file, because a) I don't think they're aware of what's going on (no replies to our e-mail yet), and b) they're a large business that depends heavily on e-mail, and I don't want to prevent them from downloading their incoming e-mail. They're actually not sending e-mail, just making connections to the SMTP server (why, I have no idea).

some info on your mail set up would help

OS, MTA, etc :)

You are going about this all wrong.

First, you should be contacting your Client to explain and source out, the situation. If eMail gets you no replies it's an excellent reason for phoning them -- yes, good Hosters will actually "phone" their Clients.

A good Salesperson knows a selling opportunity when they see one. ;)

Originally posted by Website Rob
You are going about this all wrong.

First, you should be contacting your Client to explain and source out, the situation. If eMail gets you no replies it's an excellent reason for phoning them -- yes, good Hosters will actually "phone" their Clients.
Yes, well unfortunately this client is overseas so it was a lot more practical (and time efficient) to just block their IP from the SMTP service until the situation got resolved. But thanks for letting me know what "good hosters" do, it's going on a sticky note in my office.

Maybe trying the following:
sendmail: 195.9.2. 195.9.3. 209.11.102.

It works for me :)

Saludos!