Sendmail will not send email
 

I send out a monthly newsletter to my clients about 35,000 emails per month. When ever I send the emails they will go out fine. Once I get to the next month and try to send it it will not go out. I have to change my ip address each time. I called my ISP and they are NOT blocking port 25.
Once I change my external IP addresses it will send like normal.
Anyone have any ideas ???

Thank you guys Michele

They may not be blocking that port, but if they see 35000 emails coming at once, from one address, they may blacklist your IP address, thinking you're a spammer.

No ports are being blocked.
It is very weird. I can send the newsletter out fine. When I get ready for the next one I always send a test to myself to my yahoo account. It will not come through until I change my ip address and it will send fine ANYONE HAVE ANY IDEAS ?? I play around with the domain name changing it in sendmail.cf and its intermitting ??? Sometimes it will send sometimes it wont uggggggggg !

Yes, I gave you an idea above. I understand that no PORTS are being blocked, but the ADDRESS might be. As I said, if I was running a mail relay/ISP, and I saw 35000 messages come through at once, every now and then, I'd probably assume that person was a spammer, and blacklist the address.

Since it works when you CHANGE the address, but only the one time, I'd say that could be the cause. Have you verified with your ISP that the previous address(es) you've used haven't been blacklisted as a possible spammer?