Determining deliverability

[Kevin P. Fleming]

Pat Lashley wrote:

> I've been thinking about finding the cycles to whip out a utility
> that would take a local_part on the command line; and return success
> or failure to indicate whether it is deliverable.  It would work by
> starting an LMTP session and issuing a RCPT; then RSET and QUIT after
> getting the response to the RCPT.  Having to spawn a task to do that
> is a bit ugly; but I don't think Exim has a way to do it internally.
> (Or at least not directly.  I might be able to do something with the
> built-in perl lib...)
> 

Exim 4.20 has (almost) what is needed to do this now. It can already 
do SMTP callouts to verify recipients. It can also LMTP callouts, as 
long you aren't using LMTP AUTH for delivery to Cyrus. I am using LMTP 
AUTH so I don't have to add special permissions to folders for direct 
subfolder delivery, but if you aren't, and are using LMTP over TCP/IP 
for delivery to Cyrus, then all you need is a "verify = recipient" 
clause in one of your ACLs, and Exim will make the callout for you. 
Exim also caches callout results, so it won't make repeated callouts 
for the same addresses more often than you specify.