Gmail shows a red question mark as profile photo for non-authenticated email senders:

When a Gmail user moves his mouse over the red question mark icon, the following message appears:

Gmail couldn't verify that [mydomain] actually sent this message (and not a spammer)

The cause is that there is no SPF record on your domain's DNS Zone Editor. Be sure to follow the instruction on this article to configure an SPF record and the issue will be solved!

NOTE: Feel free to check our collection of articles regarding emails :) 

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