I've been trying to get some friends signed up on my lemmy instance.
The issue is, so far nobody seems to be receiving the signup/verification emails. I am getting the admin user-signup emails, but those are sent to contact@<instance-domain>. I created 2 test users, one with a instance-domain address, and one to a gmail. The instance-domain address was there within a minute, but the gmail one has yet to arrive.
This sounds like a mail delivery problem rather than specifically a Lemmy problem. The Lemmy server configuration tells your instance how to send email; the default is to use an SMTP server on localhost.
Assuming you have a mail server running, try checking its logs. Maybe Gmail is rejecting mail from your IP address, or maybe your hosting provider or ISP is blocking port 25 by default as an anti-spam measure?
Lemmy may be having a problem as well. I cannot get the reset password link to actually send me a password reset email. I received the registration confirmation weeks ago, so I know my email is linked to the account.