Notifications not sending to BCC recipients in one specific situation

Hi — I'm experiencing an unusual problem and wanted to check if this was a known issue or a configuration error on my end.

My form has a user notification email set up. In the BCC field, I have comma-separated merge tags for three email address fields entered by the user when the form is completed. I.e.: {Email Address:1},{Email Address:2},{Email Address:3}

The notification works perfectly fine when the user completes all three address fields, or even just the first two fields. But if the user only completes the _first_ address field, then the notification doesn't BCC to that address — only the To recipient receives it.

I'm using WP-Mail-SMTP, but I've found that this problem is consistent across SMTP, PHP mail() function, etc. I'd be grateful for any suggestions!

Chris — Thanks for your help. Here's what I've found:

- If I hard code only the first address in the BCC line — i.e. "email@foo.bar,{Email Address:2},{Email Address:3}" — and then submit the form without completing the second and third address fields, the problem persists; no notification is sent to email@foo.bar

- However, if I hard code all three addresses in the BCC line, the notifications arrive reliably

- If I try the merge tags individually in the BCC line, they work fine

- I tried different orders in the BCC line, and the problem looks to be tied to the first email address in the BCC, rather than to a specific field or merge tags