Email communication is always 2 ways.
When you deliver an email, the travel path is like how you deliver a traditional mail but everything happen within few seconds.
Outgoing email path in shared hosting:
Exabytes client (Outlook/Webmail) > Exabytes mail server > Exabytes Custom (Spam Experts) -> Recipient mail server > Recipient.
When our postmaster pass the mail to different recipient, their building (mail server) will run security checking according to their policy/rules before decide to accept that mail or not.
If they decide to reject this mail, their building security guard may or may not return you with a detail in that rejection.
Some of them may put a private label on your email and let the recipient decide whether to read it or not.
Our mail servers do not have any configuration for rewriting any of your Outgoing mail transaction.
Here is some of the sample situation.
A) Email get label as ‘[Spam-pop3] ’
It would typically be due to the Spam Filtering that is included in the Singtel Corporate Broadband plan used by recipient network.
B) Email get label as ‘[***SPAM***]’
It would typically be due to the Spam Filter (powered by Apache SpamAssasin)
C) Email get label as ‘SPAM-Low/Medium/High’
It would typically be due to the Spam Filter by recipient that supported by SmarterMail.
D) Email get label as ‘SPAM’ or other text.
Custom Subject modified by a third party Security product such as McAfee (default tag for spam mail is SPAM, default tag for phishing email is PHISH), Avira and etc.
Major providers such as Gmail, Yahoo or Microsoft email products will not rewrite the subject but will move email that they identified as spam to their Junk / Spam folder.
Please provide us the full email header if you receive this kind of sharing from your recipient.