SendGrid, Mailgun, and Amazon SES are excellent services for transactional email — notifications, confirmations, receipts, and marketing to opted-in lists. They are consistently poor performers for cold outreach prospecting. The reasons are technical, not arbitrary, and understanding them will save significant time and money spent debugging a campaign that will never reach the primary inbox.
The Shared IP Problem
SendGrid's standard plans route email through shared IP pools. Your sending reputation is directly affected by the behavior of every other SendGrid customer on the same IP pool. Cold email senders, newsletter marketers, and spammers all share the same infrastructure. Gmail and Outlook have well-trained models that recognize SendGrid IP ranges and apply heightened scrutiny to email from those IPs. Even with good content and low complaint rates, inbox placement from shared SendGrid IPs is structurally inferior to Google Workspace or Microsoft 365.
The Reputation Signal Problem
Mail sent through SendGrid, Mailgun, and Amazon SES has the signature of marketing automation infrastructure — even when the email is personalized and targeted. Receiving server models classify the source infrastructure as a marketing or mass sending tool, which contributes to spam classification independent of content quality.
What Actually Works
Google Workspace and Microsoft 365 accounts on dedicated, warmed sending domains consistently outperform SMTP relay services for cold email inbox placement. These are the platforms that inbox providers recognize as legitimate business email hosts — their IP infrastructure is associated with genuine individual communication. Omni's full cold email sending infrastructure setup is described in the outbound system overview.