Authentication issue -
Blocked IP Address -
SPF/DKIM Authentication Failures:
Email Server Configuration Issues:
Email Sending Limits:
You may be limited in how many emails you send in a given period of time by certain email providers. When these thresholds are exceeded, Error Code 521 may appear.
How to resolve SBCGlobal Error Code 521
- First of all ,Verify again the password and username connected to your SBCGlobal email address. Update your password if necessary, and make sure it complies with the email provider’s security specifications.
- Secondly, Use internet tools to see if your IP address is included on any email blacklists. In the event that you are blacklisted, get in touch with your Internet Service Provider (ISP) to rectify the matter or change your IP address.
- Thirdly, Make sure your DNS settings have your SPF and DKIM records set up appropriately. If you need to update them to comply with your email provider’s specifications.
- Finally , Verify that the transmitting restrictions that SBCGlobal has set are within the acceptable range by checking them. You can request help from SBCGlobal support to raise your sending limitations if needed.