afaik, this is new.In a nutshell, AOL is throttling inbound SMTP connections.
Through about last June, I managed a list server of 2 joke lists of about 55K subscribers each. Between them, about 50K were to AOL. Apart from an intial AOL blacklisting (which the list owner got AOL to cancel), we never had any problem delivering 50K msgs/day to AOL, with 50 recipients per session. And did it within 3 hours for all 110k Msgs. (this was not IMail list server).
Estimate one msg to AOL takes 5 seconds, that's 750 msgs/hour per single SMTP process. Maybe Scott's queue kicker can get 5 or 10 SMTP processes running simultaneously, that would be 4 to 8 K msgs/hour.
Can one set Imail to send one msg per SMTP session rather than the default max of 5? If possible, this would be a registry hack. It would probably be sufficient throttling to keep under AOL's radar and keep steady flow of msgs going out, rather than horrendous 10 minutes of dead time.The workaround is to go into SMTP in Imail and set retries at 288 and the Queue timer at 10 (minutes). This means that Imail will try to send queued messages each 10 minutes, 288 times (2 days). I figured with all the testing I did, that I can get 600-700 emails per hour out to AOL. I sent sent 2500 eamils to AOL last night and watched the .LST files closely as they went out. It took 36 retries.
And since each IMail SMTP session would be spread over AOL's set of MX ip's:
# dig @205.188.157.232 aol.com mx
;; ANSWER SECTION:
aol.com. 1H IN MX 15 mailin-02.mx.aol.com.
aol.com. 1H IN MX 15 mailin-03.mx.aol.com.
aol.com. 1H IN MX 15 mailin-04.mx.aol.com.
aol.com. 1H IN MX 15 mailin-01.mx.aol.com.
;; ADDITIONAL SECTION:
mailin-02.mx.aol.com. 5M IN A 64.12.136.89
mailin-02.mx.aol.com. 5M IN A 64.12.136.121
mailin-02.mx.aol.com. 5M IN A 64.12.137.89
mailin-02.mx.aol.com. 5M IN A 64.12.137.184
mailin-02.mx.aol.com. 5M IN A 64.12.138.89
mailin-02.mx.aol.com. 5M IN A 64.12.138.120
mailin-03.mx.aol.com. 5M IN A 64.12.136.217
mailin-03.mx.aol.com. 5M IN A 64.12.136.249
mailin-03.mx.aol.com. 5M IN A 64.12.137.121
mailin-03.mx.aol.com. 5M IN A 64.12.137.152
mailin-03.mx.aol.com. 5M IN A 64.12.138.57
mailin-03.mx.aol.com. 5M IN A 64.12.138.120
... even better.
... uh oh, I think the RFC police on this list will reaching for their riot sticks. :))12:18 16:19 SMTP-(00000684) SMTP_DELIV_FAILED 12:18 16:19 SMTP-(00000684) >QUIT 12:18 16:19 SMTP-(00000684) s: s 12:18 16:19 SMTP-(00000684) s: s
( When it comes to defending against abuse, I think any tactics an MX wants to adopt are just fine, RFC's be damned. )
Since AOL MX's don't reject unknown users (ie, each AOL MX apparently does not look up each "RCPT TO: recipient" in a databaose of AOL's 30 million accounts), afaik, but eat everything thrown at them, limiting incoming delivery rate from a given ip by dropping the session is about all they can do.
If someone decides he is getting poked in the eye, waiting for a protocol-respecting opportunity to say "would you please stop poking me in the eye" is not an effective defense. Judging from our own dictionary attacks, we can assume AOL's MX's are under horrendous, multiple attacks 86400 seconds/day.
What would you do, with $millions of revenue per month at risk from subscribers who threaten to unsubscribe due to chronic mail problems, if you were Mr. Mail Admin for of AOL?
Len
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