If you are using Sumac to send bulk email and are receiving an SMTP error, it's most likely that the information about the SMTP server is configured incorrectly or not at all. A Sumac Administrator needs to set up the details of your SMTP server in the Office record (Utilities > Customize Database > Email and Office Settings).

Edit the office record, paying special attention to the fields related to Email Settings. 

If you are using a Gmail account to send bulk emails out of Sumac, try clearing and reconnecting your Google account.

If you are using an Office365 account to send bulk emails out of Sumac, try clearing and reconnecting your Microsoft account.

If you are using your organization's own SMTP details to send bulk emails out of Sumac, review and adjust these fields: SMTP Server Port; SMTP Server; SMTP Server User; and SMTP Server User Password.

Another consideration is if you are sending email during a busy time of day, is it possible that the SMTP server is busy. Wait 30 seconds and try again. When sending email, Sumac tries five times to establish a connection to the SMTP server for each email. If the SMTP server does not respond, then either the SMTP server is unavailable, or your connection to the Internet has failed.