The ‘Error 550 5.7.708 service unavailable’ often occurs on sites sending emails through Microsoft’s API. It indicates that the service is unavailable due to the sender’s email being identified as a source of spam.
In some cases, it can occur if you’re sending emails through a Microsoft tenant that’s not authenticated on your site. Or your site is missing the SPF, DKIM, and DMARC records required to verify your domain.
Resolving the Error – Solution
To fix this error, we recommend verifying that the sender email corresponds to the email address you authenticated when configuring Microsoft’s API on your site.
If there is a mismatch, you’ll need to update the email address to match to authenticated one. As an example, we’ll show you how to update the From Email setting in WP Mail SMTP.
For this, log in to your WordPress admin dashboard, go to WP Mail SMTP » Settings, and select the General tab.
After that, locate the From Email settings and ensure it matches the one you used to configure Microsoft’s email API.
You may also enable the Force From Email setting. This ensures other software on your site doesn’t override the From Email you configured.
Note: For more details, please see WP Mail SMTP’s tutorial on setting up the Microsoft SMTP server.
Another way to resolve this error is to verify that you’ve added the required SPF, DKIM, and DMARC records required to improve email deliverability. Adding these records improves your domain’s reputation and prevents email delivery issues due to low-reputation.
To learn more about these records and how to add them, be sure to check our tutorial on SPF, DKIM, and DMARC records.