Many email clients will automatically configure the appropriate connection settings for your account, but confirm that the connection settings your email client configures are the same as what's listed below.
If you're using a client that's not listed above, you can also use the following information to configure your IMAP. If you have problems, contact your mail client's customer support department for further instructions.
Incoming Mail (IMAP) Server - Requires SSL
Outgoing Mail (SMTP) Server - Requires TLS
Requires TLS: Yes
Requires authentication: Yes
Use same settings as incoming mail server
Full Name or Display Name: [your name]
Account Name or User Name: your full Google Cloud email address (username@your_domain.com)
Email address: your full Google Cloud email address (username@your_domain.com)
Password: your Google Cloud password
If your client does not support SMTP authentication, you won't be able to send mail through your client using your Gmail address.
Also, if you're having trouble sending mail but you've confirmed that encryption is active for SMTP in your mail client, try to configure your SMTP server on a different port: 465 or 587.
Also see Google’s article on iMAP Settings with 3rd Party E-mail Clients