Re: Spam Control for Mail Relay

What's the reason for that?
Possible solutions depend on the rationale for setting up such a
relay in the first place.

Somtimes the main Mailservers are not online and to not loose any mail
we want to allow our customers to use our server as a backup to queue
all messages until there server becomes online again.

The simplest solution would be just to remove the relay.

Not an option ..

If you can't do that, you need a way for the relay to determine whether
an incoming mail is addressed to a valid recipient, so that it can
reject mails to invalid recipients *during the SMTP conversation*.
How you do that depends heavily on your situation, IOW on the reason
why you need the relay in the first place. A few possibilities:
- off-line copy of destination servers' user databases on the relay
- on-line query of user database (eg. LDAP)
- SMTP call-ahead, ie. asking the recipient server in real time whether
it will accept that address


SMTP call ahead is a nice idea but will fail if the server is down so i
think it would be a mood point. Also since all customers servers do not
expose there user Data via LDAp and it might be not avail durring
maintance, i think the only option would be a local copy of all users.
My question now would be where to store it ? LDAP or hash Table, idealy
i would like to place it in a mysql table but i dont think thats
supported.
What is the performance impact hash table versus LDAP and how many
records can i actually put in a hash table without getting performance
issues ?

.

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