C#, here? not here?

['Bruno]

You dont need the credentials of who you're sending it to, just their email lol.
You need your own credentials to login on the smtp server and then you're able to send emails

oh ok, that was a thing that was confusing me... i really thought that i would need Their credentials, ok. thank you

[B1ackAnge1]

Nope not needed - in that scenario you're describing it's really no different than you sending some people an email - all you need is your credentials (or the person sending it) so it looks like option 'a' would be the way to go