I use sp_send_dbmail to e-mail to groups of users. There can be hundreds of addresses at a time, all of which I am including as BCCs on one mail. Some users at certain domains do not receive the e-mail, and it does not show up in their spam folders. I know that some mail systems block incoming e-mail that has many addresses in the BCC field because it looks like spam. I am assuming this is what is happening.
I believe the ideal solution is to send the e-mails to smaller groups, or to send e-mail individually to every user using the TO field. However, I can't seem to find any guidelines. What is a safe number of BCC addresses to have in a single e-mail without it getting rejected as spam?