But the following function does not send the email to the address in bcc (eulixo@gmail.com) while the email sent to the "to" address is properly sent and received.
Very odd bug and behavior, it looks like you set up everything correctly.
What is even more unusual is that the response has the eulixo@gmail.com in both the 'to' and the 'accepted' section. Where you mentioned that the email was not sent to that user and instead was sent to the non-bcc email
Does the host provider have logs of the emails you sent? Are you self hosting Retool? If so, what version are you on? I am testing out SMTP/BCC on my own currently to see if I can reproduce this bug.
You may need to check with your service provider(smtp.titan.com) to see if the error might be coming from their end.