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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?

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The BCC field is only evaluated at the first mail server and then the mail gets broken up at that mail server for each recipient. So no destination server will know how many other recipients were in the original mail.

The only server that can reject your mail because of too many BCCs would be the one you contact directly.

So the answer to you question is: unlimited.

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By "first mail server", do you mean the SMTP server that my organization uses to send the mail? To clarify, the majority of recipients are receiving the e-mail, but there are a handful of domains that don't seem to receive it. If our SMTP server did break up the mail immediately, wouldn't the e-mail get blocked from going to ALL users? –  SomeGuy Oct 31 '11 at 17:27
    
@SomeGuy The mail splits at the first server. I can't answer which server this is, but probably the one in your company. Sending to multiple recipients does not mean "all or nothing". It means "for as many as possible", and the rest bounces. –  mailq Oct 31 '11 at 19:22
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At the request of the SMTP server administrator, I tried breaking up the e-mail and sending out one per person directly, and that seemed to do the trick. Something on our SMTP server must have been detecting the mails as spam.

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