Has anyone run into this problem? I have a 1500 person mailing list and if I use a script to send the email filemaker crashes with an unknown error.

I've tested this on more than one system with the same results. I'm not sure what the exact number that will cause a failure but it's about 1000.

I've had to split the email into smaller groups using 3 scripts with a constrain record set step.

Are you looping thru a found set using Send Mail?

no. The customer just wants all 1500 in the to line of a single email.

Why is that a requirement?

Yeah, sounds like a bad idea. An email with over 1000 (or even over 15) is likely to get stopped by spam filters, or at least is more likely to be stopped by spam filters.

Not sure why they require it that way. I think they have been blocked in the past.

Check your win.ini file in the windows folder. It should contain the two lines, [Mail] and MAPI=1. Some internet security programs and IE7 actions can remove these entries. When they are removed from the win.ini file the 'send mail' action in FileMaker will crash the application.

(This info was found on a TechNet post. Hope this isn't breaking some protocol somewhere sharing it here).

I checked and they have those settings. I found out outlook has an 8kb limit for addresses going in the to, cc, and bcc. This is probably why it crashes. I split the email into 3 smaller ones using a member_number serial number field I added to divide the groups up.