To manage your email account’s mail services open Emails → domain name and click on ⋮ near the email account in question:
There choose Settings:
There are the following options:
Disable email account: fully turn off all accesses, like sending, receiving emails, and logging in to your account via Webmail
Suspend access: turn off logging in to your email account. You won’t be able to access your emails
Suspend receiving: turn off receiving emails. You won’t be able to receive any emails, but will be able to send them
Suspend sending: turn off sending emails. You won’t be able to send any emails, but will be able to receive them
If you are using PHP scripts to send mail, check this article: How to manage Mail Services for Web hosting Emails?