Sending CDONTS Mail Within Loop

I am trying to send e-mails to customers in a database. Each e-mail is customised for each customer, so I cannot simply copy all customers on the same e-mail. My logic loops through the appropriate recordset and attempts to send a notification e-mail to each customer. The problem is that about 10 - 20% of the e-mails do not get sent! (I know this because I :bcc myself on all the e-mails.) I also know that there is no problem with the e-mail addresses because when I try again to run the program with the same addresses but a smaller list of customers, those mails go out just fine.

The program generates a report which shows that it tried to send all the appropriate e-mails, but in reality several of the mails were not sent. What's interesting is that all of the e-mails near the beginning of the program execution get sent. But as the program goes on, more and more get skipped. It seems that CDONTS cannot keep up with the program execution.

Does anyone know of a way to solve this? What would be great would be a DO... WHILE loop that kept trying until the e-mail was sent successfully. But, for that approach to work, there would have to be some way for the program to check if the e-mail had gone out successfully. Another option would be a loop that waited until the *previous* e-mail had been sent successfully before attempting to send the next one.

Does anyone know of a way to test either of those conditions or of an alternate approach to avoid this problem I am having?