Many e-mail providers such as Hotmail, AOL, Yahoo and most others use aggressive spam filtering technology, this technology has a higher rate of blocking genuine non-spam e-mail from sites or e-mail accounts on a shared-hosting server.
 
There are many reasons why an ISP or provider may block, flag or filter genuine e-mail and often, there is nothing you as the sender or we as the host can do to prevent this from occurring.
 
Some of the reasons for this result include:
 
- HTML CONTENT : The more HTML, the less likely your e-mail will be received
- KEYWORDS : Most filters flag e-mails and raise their spam score based on the presence of keywords in messages
- VOLUME : Too many e-mails have been received by the provider/destination from the sender or server in a given period of time
- ATTACHMENTS : Suspicious or large file attachments may cause filters to flag or delete your e-mail
- TRUST SCORE : The sending server, domain or user may not have a high enough trust rank for the destination server, domain or user
- VIRUS CONTENT : The destination server detected a virus in your message or the threat of one
- OTHER : The vast majority of providers employ rules, settings and methods for detecting spam wholly proprietary to their platform of which your e-mail falls victim
 
What is a site owner to do?
 
Visit :

https://www.mail-tester.com/

And then create a support ticket with iFastNet support showing your mail tester results page, we can use this to carefully diagnose your email and fix any problems.

Best regards