Email vendors
18 distinct email vendors appear across 314 companies in the VendorStacks index — not inferred from tracking pixels or job posts, but read from what each company publishes about itself. SendGrid leads at 39.8% adoption; the top five together account for 99.1%.
Most used email vendors
Ranked by how many companies name each vendor in their own published documentation. Share is of the 314 companies we have a email vendor for.
| # | Vendor | Companies | Share |
|---|---|---|---|
| 1 | SendGrid | 125 | 39.8% |
| 2 | Mailchimp | 57 | 18.2% |
| 3 | Resend | 50 | 15.9% |
| 4 | Mailgun | 42 | 13.4% |
| 5 | Marketo | 37 | 11.8% |
| 6 | Courier | 37 | 11.8% |
| 7 | Postmark | 27 | 8.6% |
| 8 | Customer.io | 22 | 7% |
| 9 | ActiveCampaign | 20 | 6.4% |
| 10 | Amazon SES | 19 | 6.1% |
| 11 | Braze | 17 | 5.4% |
| 12 | Klaviyo | 17 | 5.4% |
| 13 | SparkPost | 11 | 3.5% |
| 14 | Iterable | 11 | 3.5% |
| 15 | Mailjet | 8 | 2.5% |
| 16 | OneSignal | 7 | 2.2% |
| 17 | Loops | 5 | 1.6% |
| 18 | Knock | 4 | 1.3% |
What else these companies run
Of the companies with a email vendor, this is the share that also disclose a vendor in each other category — the co-adoption pattern behind most segmentation work.
Companies with a email vendor
| Company | Email vendors |
|---|---|
| careerservices.fas.harvard.edu | SendGrid |
| arcticwolf.com | SendGrid |
| milosolutions.com | Mailchimp |
| vcboom.com | Resend |
| everestgrp.com | Marketo |
| maslool.ae | Amazon SES, Mailchimp, SendGrid |
| baaed.com | SendGrid |
| viceroynm.com | Resend |
| roxyapi.com | Resend |
| finsweet.com | SendGrid |
| medstack.co | SendGrid |
| mitti.com | Braze, Customer.io, Mailchimp, Mailgun |
Showing 12 of 314. One call returns the full set with evidence rows, source URLs and refresh timestamps.
curl "https://api.vendorstacks.com/v1/prospect?category=email" \ -H "Authorization: Bearer vr_live_…"
How this is measured
Companies disclose their own vendors — subprocessor lists, trust centres, security pages and privacy documentation name third parties by regulation or by policy. VendorStacks crawls that public surface, renders JavaScript pages and PDFs, and matches a deterministic taxonomy of 24 categories against what the company itself published. No tracking pixels, no DNS fingerprints, no guessing from job posts. Every match keeps the sentence it came from, which is why a share figure on this page can be traced back to a specific document on a specific company's site. How it works →
Frequently asked questions
- Which email vendor is most widely used?
- SendGrid appears in 125 of the 314 companies we have a email vendor for — 39.8% of them. The next four together account for 59.3%.
- How do you know a company uses a email vendor?
- Because the company published it. Subprocessor lists, trust centres, security pages and privacy documents name vendors by law or by policy. We extract the vendor name and keep the sentence it came from, so every match has a quotable source rather than an inferred fingerprint.
- How current is this data?
- The most recently refreshed company in this category was updated 2026-09-10. Disclosure pages change slowly — usually when a vendor is added or dropped — and we re-scan on a rolling basis.
- Can I get the full list rather than a sample?
- Yes. One API call returns every company in this category with its vendors, the evidence row, and the source URL. A free key includes 25 credits and each lookup costs one.