Can't send to multiple bcc's


New Email
I'm wondering if anyone here can help. I have a small cleaning business and I have bought an email list of local firms to send to, about 2,500 addresses.

When I try to send a message to around 100 at a time using bcc for the addresses I get a message similar to:

The message could not be sent because one of the recipients was rejected by the server. The rejected e-mail address was ''. Subject '', Account: '', Server: '', Protocol: SMTP, Server Response: '550 5.1.1 Adresse d au moins un destinataire invalide. Invalid recipient. OUK204_418 [418]', Port: 25, Secure(SSL): No, Server Error: 550, Error Number: 0x800CCC79

I am using outlook express, my ISP is and my email host is
I would be grateful for any suggestions
Many thanks to all