There can be a number of reasons for this. Sometimes a message will get marked SPAM because of specific "spammy" types of words in the mail. Words like pharmaceutical or charity or loan etc in combination can increase the chance of an email being tagged as SPAM. Even having too many links in an email can increase a spam score.
Sometimes a domain name or IP address can get flagged as having sent SPAM. We actively monitor the integrity of our email servers IP address for this reason and pro-actively take action if there is ever any question about the integrity of the service.
There are three DNS settings that can also help your emails land correctly in someone's inbox. These settings are known as:
- SPF
- DKIM
- DMARC
By default we set up both SPF and DKIM settings for any new account hosted with us. These settings will boost your success rate if you send email using our recommended outgoing server settings.
The dmarc settings however you can add using the cpanel control panel.
Goto: "DNS Zone Editor" - "Manage" - "Add Record" - Add DMARC record".
The default settings are a good starting point and you only need to add an email address under the "Optional Settings" - "Send Aggregate Mail Reports To". You can then monitor the incoming reports and adjust your settings.
More info: https://dmarc.org/overview/