which email service support BCC in email?

you mean this in Gmail right? it works fine

Gmail 

Almost every email provider support bcc

I guess OP's query was whether Bcc is working or not in Gmail rather than whether Gmail has Bcc feature or not, as if you have the To as the same inbox address and add Bcc then it shows Bcc in your inbox i.e. say [email protected] is the Gmail (own) you are using to send email (for testing) and if you have To as [email protected] (own) and Bcc - [email protected] (Recipient 1) then when you get email in Test1 it shows the Bcc, however if you have To - [email protected] (Recipient 2) and Bcc - [email protected] then Test3 will not have Test2 in his Bcc, in short, you cannot test whether Bcc is working or not with the same email id inserted in To

my above story is totally irrelevant unless OP's replies what or why or how he is saying Bcc is not working in Gmail 😀😃

BCC IS NOT WORKING IN GMAIL
https://support.google.com/mail/thread/15880130...

I think all mail services give this option by default... Never tried though!