Marketing emails not sending due to unexpected SMTP configuration errors

sandeep_erp
Thu, 19 Jun 2025 16:38:00 +0000

The 550 5.7.1 error specifically indicates authentication failure at the SMTP level, not just DKIM. This suggests your sending infrastructure might be rejecting emails because the DKIM signature doesn’t match what the receiving server expects. Are you using a custom sending domain or HubSpot’s default? If custom, double-check that your SPF record includes HubSpot’s sending servers (include:_spf.hubspot.com). Without proper SPF alignment, even valid DKIM won’t help with authentication.