I have a moderator for the mail listing complaining that their customers(subscribers) not receiving the E-mails. Out of 2500 subscribers there are around 330 subscribers who had received the E-mails from the mail listing address sent by the moderator based on the delivery logs. Furthermore, the delivery log only shows 2 hour delivery range for the particular mail listing address, yesterday and up till now no more delivery seen for that mail listing; as well as, spool not showing any stuck e-mails for that mail listing address.

So, is this a bug or there's a limitation to the numbers of subscribers delivered?