sendmsg.io vs SendGridA Modern Alternative

DNS records — SPF, DKIM, DMARC

Add three records to your sending domain's DNS. SPF gets an include:_spf.sendmsg.io entry (you can keep SendGrid's include during the parallel-sending window, since multiple includes are valid up to the 10-lookup limit). DKIM is a CNAME record sendmsg.io provides per domain. Point scope1._domainkey and scope2._domainkey at the values shown in your dashboard. DMARC you probably already have; just confirm the policy is at least p=quarantine with alignment set to relaxed for both SPF and DKIM. Propagation is usually 10-15 minutes; the sendmsg.io dashboard verifies all three records and flags misconfiguration before your first live send.

API endpoint swap — REST mapping

Both APIs are JSON REST. SendGrid's POST https://api.sendgrid.com/v3/mail/send maps to POST https://api.sendmsg.io/v1/email/send. Field renames:

// SendGrid
{
  "personalizations": [{"to": [{"email": "[email protected]"}]}],
  "from": {"email": "[email protected]"},
  "subject": "Hello",
  "content": [{"type": "text/html", "value": "<p>hi</p>"}],
  "dynamic_template_data": {"name": "Alex"}
}

// sendmsg.io equivalent
{
  "recipients": [{"email": "[email protected]"}],
  "from": {"email": "[email protected]"},
  "subject": "Hello",
  "html": "<p>hi</p>",
  "variables": {"name": "Alex"}
}

Replace SENDGRID_API_KEY with SENDMSG_API_KEY in the Authorization header (Bearer scheme on both). If you'd rather not touch application code, SMTP relay works identically. Swap the host from smtp.sendgrid.net to smtp.sendmsg.io and update the credentials. Most teams put a feature flag in front of the call so 5% of traffic flows to sendmsg.io for the first day, ramping to 100% over the parallel-sending window.

Suppression list import — bounce and spam DBs

This is the step teams skip and regret. SendGrid keeps your hard bounces, unsubscribes, spam reports, and blocks across four separate suppression endpoints. Pull all four:

GET /v3/suppression/bounces
GET /v3/asm/suppressions/global    # unsubscribes
GET /v3/suppression/spam_reports
GET /v3/suppression/blocks

Combine into a single CSV with columns email,reason,suppressed_at and bulk-upload to sendmsg.io via the dashboard or POST /v1/suppressions/bulk. Keep both sides in sync for the 2-week parallel window: any new suppression on SendGrid gets carried over to sendmsg.io and vice versa. We have a CLI helper that handles the daily delta if your list is large.

Warmup strategy — the 30-day ramp on the new domain

If you're moving to a fresh sending domain (recommended for the cleanest reputation story), plan for 30 days of graduated volume. The schedule we publish in the 2026 Deliverability Playbook: day 1 starts at 50 emails, day 2 doubles to 100, days 3-7 ramp through 200/500/1000/2000/5000, then days 8-30 follow an engagement-weighted curve toward your target volume. sendmsg.io's Cortex automates the daily ramp and slows specific ISPs that show deferral pressure without halting the whole schedule. Outlook deferring on day 8 doesn't pause your Gmail ramp.

If you're keeping the same sending domain (reusing the established reputation), the warmup compresses to 7-10 days because the domain's history with major ISPs carries over. Either way, the engagement-driven daily limit is the difference between a warmup that ends on time and one that quietly stalls because nobody noticed Gmail had been deferring for three days.

Validation period — 2 weeks of parallel sending

Run both platforms in parallel for two weeks. Split traffic 50/50 if you're confident in the swap, 90/10 if you're cautious. Compare inbox-placement seed tests on both platforms. A 250-address seed list across Gmail, Outlook, Yahoo, and corporate domains will tell you which side is winning the placement battle. The seed tests should agree within 2-3 percentage points; if sendmsg.io comes back materially worse on a specific ISP, that's the signal to investigate before cutting over fully.

Other metrics to compare during validation: open rates by ISP, bounce rates by bounce category (transient vs hard), complaint rates per million sends, and click-through if your campaigns have consistent CTAs. Once two consecutive weeks agree, flip the feature flag to 100% sendmsg.io and decommission the SendGrid account at the end of the next billing cycle.