Hello @TatianaSantolloL ,
Some troubleshooting questions:
Was this originally occurring with an email's first send out, or for a resend version?
Are the required elements of the email's header filled in (from address, reply-to address, subject line, from name)?
Have you recently made updates to your account's email authentication that might impact the verified addresses (switching from ccsend to self-authentication, or vice versa)?
Does the email contain any specialty blocks that were copied over from its previous version - feedback blocks, RSVP blocks, or product blocks?
If you have a specialty block like a feedback, RSVP, or product block, do they contain emojis or special characters?
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