When sending a bulk email using phpmailer, is it better to send one email with multiple BCCs or multiple individual emails?

Question

When sending a bulk email using phpmailer, is it better to send one email with multiple BCCs or multiple individual emails?

I'd like to know the effect on performance and the email being treated as SPAM by the client server.

Answer 1

It very much depends. It's largely going to be up to the whims of the SMTP server you're sending through (or the mail API you're using) and any SMTP servers between there and the final recipient.

For the most part, each recipient (To:, Cc:, Bcc:) of an email sent with multiple recipients receives an identical email. For efficiency, normally an email that is sent to multiple recipients at the same domain will be sent once, addressed to multiple recipients, and the receiving email server will handle delivery to the mailboxes of each recipient. (Your local email server should automatically handle doing this, because it wants to do as little work as possible.) So from a performance standpoint, it's better to send one email with many multiple recipients.

For spam prevention, your local SMTP server, any intermediate SMTP servers, and the destination SMTP server, may or may not treat differently one email addressed to many recipients and multiple identical emails sent to a single recipient each.

In general, if you are not actually in the business of sending emails, you should let someone else worry about that for you instead. There are many reputable bulk email sending services that can handle this for you inexpensively (many even free below a certain threshold) and you won't have to worry about maintaining your own mail servers or your domain becoming blacklisted because someone thought you were sending spam. Further, because these services are well known, reputable, and take spam very seriously, it's much less likely your email will be flagged as spam (unless you actually are sending spam).