[Mailman-Users] Mailman list size limitations?

[Joshua Beall]

Hi All,

I have a client who wants to setup a very *large* mailing list.  Right now 
she has about 4500 people on the list (including myself).

However, she has reported that people aren't getting her emails (she sends 
only about one per month), and she's tried to send two so far.  They show up 
in the archives, so I know that they are at least being received by mailman. 
Furthermore, I have been getting them - so it *seems* like it is working.

But she absolutely insists that they are not going out, saying that she has 
asked other people who are subscribed to the list, and they have not 
received her message.

Is there an error log I can take a look at it?  And also, do you know 
offhand if I am asking for trouble with such a large list?  Are there 
problems that crop up when I have such a large list?

If mailman is not able to handle such a large mailing list, what do you 
recommend?  I would prefer something open source that will run on a LAMP 
stack.

Thanks for any feedback!

Sincerely,
  -Josh