Adding an SES email as a Gmail alias

Edit:

I finally figured out what was going on. I'm 100% new to AWS, so this may be silly to some but it was something that I apparently overlooked completely. I was using the inbound endpoint to set up outbound emails. I simply went to the list of endpoints (https://docs.aws.amazon.com/general/latest/gr/ses.html) and got the corresponding outbound endpoint and we're good to go. I'm leaving this here in case anyone else has that silly moment going on so they can find out what they're doing wrong.

Original question:

We've set up our domain through Route 53 and have set up email receiving through SES already. We can receive emails correctly.

When we try to add the same email address to Gmail as an alias, in order to have outbound emails as well, we obtain the credentials from Amazon SES > SMTP settings and, when we attempt to connect from Gmail's end using port 25, we get the error below:

Authentication failed. Please check your username/password.
Server returned error: "Unspecified Error (SENT_SECOND_EHLO): Smtp server does not advertise AUTH capability, code: 504"

It's clear we're doing something wrong, but we're unsure what that is exactly, and we're unsure what else we can try.

Any help would be appreciated.