Mail Sending Queue

Question

What would be the best way to create a queue for outoing SMTP messages? Or does one already exist?
Here's my problem, I've developed an app with email-capable notices, error messges, and reminders. It can deliver an email an hour or up to 100 in a minute depending on what's happening. I originally started with a method I'd created to send the email via Transport(send) to my ISP's SMTP server. The first obstacle was the performance, it took anywhere from 1-25 seconds to deliver the messages. So, since I'm not 100% concerned if every email gets there I created a Thread object to handle the emails so that I could continue.
Then I noticed that some email weren't getting to their destination when the load went up. I saw that anything after your tenth message in a 2-minute period (or something like that) would get dropped. So, in the catch() in my Thread's run() method, I would call run() again recursively up to 10 times to try the messages again. I could send more reliably not, but not more than about 75%.
Then I looked at the SMTP server. I installed a local one and this improved things dramatically. Since, it's dedicated it will churn through messages at an average completion rate above 99% -- and I log all failed messages. This works now, but I can't guarantee everyone a dedicated SMTP box...
What I'd like is a way to guarantee me 100% message success. I want some kind of queue that pops the top message and tries to send it up to a maximum number of retries, or signals an exception, before it moves on to the next message. Does this exist already somewhere, or what would be the best way to do this so that JavaMail would be intelilgent enough to read the SMTP responses to know that the message was successfully queued up?
Thanks.

Answer 1

Or do you want some way of making sure that when the
SMTP server accepts a message, it really got the
message? That isn't what you asked, but that seems to
be the problem you are trying to solve. At any rate I
have no idea how to compensate for unreliable
servers. Except... if you are creating one Thread per
message (it doesn't sound like it but maybe I don't
get it), you may be flooding the server at times. If
so then try to limit the number of simultaneous
threads.This is exactly what I want. This is just my initial impression, but it seems like Javamail is quick to throw exceptions. I'm looking for a more robust transport mechanism -- I want to "set it and forget it." Can you make a call to the JavaMail API that would tell it to retry sending on its own for non-fatal errors, i.e. Code 450 ~ server busy status?
I do create a Thread for each email right now, at least with my dedicate SMTP box, it's not causing a problem. It's admin report is telling me that I'm only ever getting to 7% of it's concurrent session limits. I would like to have a queue with a definable number of "sender threads" to pop the messages and follow their progress.
So, to sum it up in one long sentence, I'm looking to see if there's a pre-canned mechanism out there which implements JavaMail which is robust enough to listen to the SMTP return codes and follow a message's lifecycle to guarantee either message delivery or failure only due to either connectivity problems to the SMTP host or to invalid addresses so that I don't have to parse all possible exceptions and SMTP error codes to make resubmission decisions.
Thanks in advance and sorry for my long-winded diatribe...