Hello,

I am using Symfony Mailer with two configured transports:

framework:
    mailer:
        transports:
            main: '%env(MAILER_DSN)%'
            tracking: '%env(MAILER_DSN_MONOLOG)%'

After reading the Symfony Mailer documentation, I could not find a way to log which transport was actually used for sending each email when using custom X-Transport header.

I have enabled a dedicated Monolog channel for mailer logs:

monolog:
    channels: ['mailer']

But this only logs basic email info, not the actual transport name or DSN that was used to send the message.

How can I reliably log the transport used for each email (including the transport alias or DSN) using Monolog or an event subscriber?

Thank you for your help!