Email rejected

When our client emails us they get the message below and we do not receive their email of course. Is this a problem on their end or ours? gave this error:
( []:4058 is currently not permitted to relay through this server.
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Paul MacDonaldDirector, Information SystemsCommented:
Do you own  If not, the problem is on their end.  If so, it sounds like they're trying to send mail using your server as their SMTP host (which is, evidently, prohibited).
Use the mail server tests on

Get their mx records and do a basic telnet test:

(in command line)

telnet 25
mail from:
rcpt to:

Note the output.

Then try the reverse. The route with the error - that'll show you the end that has the problem :)

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