[mothered]

The issue is with a particular email content i try sending to many, i suspect it's an issue of keywords that are flagged like you said, i can't send the same mail with my webmail (namecheap) or Gmail anymore cos it ends up in the spam folder

i suspect it's an issue of keywords that are flagged like you said

Given It's only relative to one particular email message, the keywords used are definitely the cause.

You need to Identify exactly what's being flagged as spam. Create a Gmail account and send the email message to yourself. Through trial and error, eliminate certain keywords a little each time until you find those responsible for being marked as spam.

but i wanna ask again, is there any possibility of my webmail (namecheap) restricting my mails cos they feel am spamming?

Are you able to send a single email (or selected emails) via Namecheap, without any restrictions/spam detection whatsoever?