Due to changes in server settings, different errors related to e-mail servers may appear. One of them is "SPF fail - not authorized" error.

"SMTP Error: The following recipients failed: example@example.com (5.7.1 : Recipient address rejected: Message rejected due to: SPF fail - not authorized. Please see http://www.openspf.net/Why?[your-information-inserted-here])"
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Simply put, the domain example.com sends e-mails using sendgrid.net However, according to the example.com domain, sendgrid.net (168.245.48.213) is not in the authorized and trusted list which is used to send the e-mails and therefore all e-mails are rejected.
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There are 2 possible solutions for this problem:

1. First option is to contact your e-mail service provider to adjust their settings. Simply ask them to add ip4:168.245.48.213 include:sendgrid.net to the trusted exceptions list through which it is okay to send e-mails. Once this has been done, you should be able to send e-mails normally. Example txt record is: 

If you open the url you received from the error message, it explains in detail of what should be done as well. If you forward this information to your service provider, it should solve the issue.

2. Second option is to change the server settings in your System Management -> E-mail settings, so that you use your own outgoing e-mail server. Insert the necessary information and click "Save". You are now using your own e-mail server for sending e-mails.