Hi @VisionDigital,
Thank you for reaching out!
If I’m understanding properly, you are experiencing this issue with sales emails (1:1 emails) sent to contacts in your CRM correct? Please correct me if I’m wrong 
When you send a 1:1 email through HubSpot, you are sending the email through your email client’s (Outlook, Gmail, etc) rather than through HubSpot’s server which would be the case for marketing emails.
The “Smtp; 550 High probability of spam” error is likely related to the recipient’s security settings and software since it believes there is a high probability of it being spam. This help article goes into further detail on this.
- It’s possible the tracked links in the email are the cultprit (all emails sent from the CRM directly will be tracked). The email recipient could try temporarily disabling tracked links in the account to see whether or not that’s the case.Turn off one-to-one email tracking or attachment logging
- If the email is successfully delivered from HubSpot with tracking disabled, it suggests the email tracking links applied to the email are the issue.
I would also recommend trying to contact the individuals outside of email to see if they can add your email address to their allowlist, so that their email security isn’t blocking your emails.
Hope this helps!
Best,
Kristen