[CentOS] Re: Postfix smtp freezing

[Ken Price]

> Should I use the graphical update or just yum update?
> Also are there any updates I should be concerned about?
> Should I update now, or after I resolve the smtp issue?

RHEL has a decent GUI, however you will be better off ignoring it and  
getting familiar with administering the box via the command line.   
Just my opinion.

I'll give my two cents and retire for the evening.  I've tried  
multiple times from 3 different locations (Atlanta & Seattle) to  
connect to MAIL.MEDVOICE.COM on port 25 ... which I'm assuming is your  
problem server.  I get inconsistent results.  Half the time I get a  
near immediate (<2 seconds) 220 prompt.  The rest of the time I get >  
10 seconds or timeouts.

I'm not saying you shouldn't update your system.  You should.   
However, I'd start by looking at the following to solve your SMTP  
problem.

1)  Your bandwidth utilization.  You have enough left over?  Probably  
yes.  But DSL is sometimes "dirty".
2)  Your server resource utilization.  You have enough CPU and memory  
in that box?   Probably yes.
3)  Who does your DNS?  Looks like Qwest is authoritative for your  
domain, do you use their recursive DNS servers too?  If yes, this  
could be a problem.  If you don't already, RUN YOUR OWN RECURSIVE DNS  
for your server!!
4)  Do you experience this problem more during certain times of the day?

Email clients are fickle and have short timeouts.  When this problem  
pops up again, try telnetting into your mail server, port 25.   
Timeout?  Error?  What?  If so, SSH into your server and locally  
telnet into port 25.  Do you experience the same problem from there?

Bandwidth and DNS are the likely culprits.  Doesn't mean, however,  
that your SPAM has increased and is using all available SMTP  
processes.  That also explains the timeouts as the email client has to  
wait for an available process.

I like MailScanner.  It's easy to setup and gives default security to  
novices, while giving enough flexibility to experts.  However, it's  
not efficient unless you have an someone who knows what they're doing  
at the helm.

-Ken