Hi @fabio mas ,
Welcome to our forum!
As i know, there's several factors which may cause this issue, just like Spam Trigger Keywords, Bad HTML Code,.ect.
How and what can be done?
You can contact the recipients to add your company domain or company senders to Safe list. Email addresses and domain names in the Safe Senders List are never treated as junk email, regardless of the content of the message. More information: Block or allow (junk email settings).
Hope the above help!
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