Keep in mind that emails have a scoring system and each provider manages a SPAM filter according to that score, when writing an email note the following points by which an email can be detected as SPAM :
Do not write the whole subject in capital letters
Do not use many exclamation or question marks in the subject
Do not use the "$" sign at the beginning of the subject
Do not use e-mail addresses in the subject
Do not include the words "free" or "viagra" in the body or subject of the message
Do not include more images than text in the body of the mail
Do not write the body of the message in HTML using very large fonts
Do not write the body of the message in HTML using a font color similar to the background color
Do not send mail from an email address that starts with many numbers
Do not send a subscription link or unsubscribe
Not having a signature full of images separately
Send the email both in text format and in html
Also, keep in mind that the recipient emails work under their own anti-spam policy, so there will be entities that take the emails as such, the user must include the recipient's email on their desired white list of emails. < / p>
Finally, keep in mind that from your cPanel you can manage whitelists, blacklists and activate or deactivate the anti spam filter.