If your email software is unable to use SMTP authentication (e.g. it cannot use an SMTP username/password), you can choose to authenticate your emails based on the IP address of the sender (we call this IP Authentication) or the From address of the sender (we call this Address Authentication).
IP Authentication
Note: available for accounts on paid plans.
IP Authentication can be enabled on the 'Sending > IP Authentication' page in your SMTP2GO control panel.
It allows you to specify IP addresses from which emails are allowed to be sent without using any SMTP username/password. This can be used if your email software is unable to authenticate with an SMTP username/password and the computer you are sending your emails from has been assigned a fixed/dedicated IP address.
Any attempt to send an email coming from one of the IP addresses you specify will be sent, and assigned to your SMTP2GO account.
View the IP Authentication article for full information.
Address Authentication
Note: available on request for accounts on paid plans.
Emails can be authenticated based solely on the sender's email address. Contact our support team if you require this feature to be added to your account. It is generally not recommended due to the low level of security involved.
Address Authentication allows you to specify email addresses that are allowed to send emails without using any SMTP username/password. If we receive an attempt to send an email coming from one of the email addresses you specify, we allow the email to be sent, and assign it to your SMTP2GO account.
For added security when using Address Authentication, we highly recommend you utilize the "IP Allowlist" feature which allows you to restrict sending through your account to only be from the IP addresses you list. If any unlisted/unauthorized IPs try to send through your account they will be blocked with the following error "550 that IP address on this account is not allowed to send".