| Altvia altvia.com | Private Equity | Email message delivery and mailing statistics | USA |
| Appointlet appointlet.help | Productivity | Transactional Emails | United States |
| Aptible aptible.com | DevOps, HealthTech | Email | United States |
| Arista arista.com | Networking and Cloud Infrastructure | Customer Support | USA |
| Assistiv Labs assistivlabs.com | Accessibility Technology | Email delivery system | United States |
| Aureliuslab aureliuslab.com | Research and Insights | Transactional email | United States |
| Bolddesk bolddesk.com | Customer Service Software, AI-driven support | Email to ticket inbound processor | United States |
| BoldSign boldsign.com | E-signature | Sending transactional emails on behalf of the SaaS provider | United States |
| BrowserStack browserstack.com | DevOps | Email notifications for enterprise customers | USA |
| Buttondown buttondown.com | Email Marketing | Email delivery and transactional email services | United States |
| By Sprinto learnwise.ai | EdTech | Customer Service | United States of America |
| Ceros ceros.com | Content Creation/Marketing Tech | Email service | — |
| Chameleon chameleon.io | Productivity | Delivers transactional emails | US |
| Chatling chatling.ai | AI/ML | Email delivery service | United States |
| Chroma trychroma.com | Data Analytics, AI/ML | Email Processing | USA |
| Classet classet.org | HR Tech | Stores email content, metadata, and delivery logs for transactional email services. | Unknown |
| Clay clay.com | Data Enrichment and AI Solutions | Email service provider | USA |
| Clerk clerk.com | DevOps | Clerk offers Postmark as an opt-in email provider for verification and transactional email messages, not applicable to most instances. | USA |
| ClientSuccess clientsuccess.com | Customer Success Software | Email Service Provider | United States |
| Credly credly.com | EdTech | Used to send invitation emails to Learners | EU |
| CustomerOS customeros.ai | Marketing | Cloud email service | USA |
| Dealroom dealroom.net | Fintech | Email delivery service | United States |
| Duckbillhq duckbillhq.com | Cloud Cost Management | Transactional email | United States |
| Employ Inc. employinc.com | HR Tech | Messaging & Notifications | USA |
| Fieldguide fieldguide.io | AI/ML, Audit, Advisory | Transactional emails | USA |
| Fillout fillout.com | Productivity | Email | US |
| FlyCode flycode.com | Fintech | Email platform for payment emails | USA |
| Fortrabbit fortrabbit.com | Cloud Infrastructure | Transactional e-mails | USA |
| Foursightonline foursightonline.com | Productivity | Transactional Email Delivery | USA |
| FreeAgent freeagent.com | Fintech | Email delivery service | United States |
| Happl happl.com | HR Tech | Outgoing email server | EU |
| Heron Data herondata.io | Fintech | Other Service functions | USA |
| Hook0 hook0.com | DevOps | Automated emailing | USA |
| Imitate imitate.email | — | Transactional email service | Global |
| InEvent inevent.com | Event Management Software | Email processing as part of a global email delivery network | Europe |
| InEvent inevent.us | Event Management Software | Email processing as part of a global email delivery network | Europe |
| Infracost infracost.io | Fintech | Sending user emails | US |
| ioZen iozen.ai | AI/ML, Lead Generation, SaaS | Transactional email (notifications, invitations, alerts) | United States |
| IP Geolocation API ipgeolocation.io | Cybersecurity | Transactional email service | United States |
| JazzHR jazzhr.com | HR Tech | Messaging & Notifications | USA |
| Jobvite jobvite.com | HR Tech | Messaging & Notifications | USA |
| Kleio kleio.ai | AI/ML | Transactional email delivery provider | EU, US |
| Kyro kyro.ai | Construction Tech | Email delivery service | Not specified |
| Lever lever.co | HR Tech | Messaging & Notifications | USA |
| Loadster loadster.app | DevOps | Outbound Email | USA |
| Luma luma.com | Event Management | Email delivery | United States |
| Memberspace memberspace.com | SaaS, Membership Management | Email | Not specified |
| Memberstack 2.0 memberstack.com | No-Code Tools | Email Marketing Services | USA |
| memoQ memoq.com | Translation Technology | Customer Service | USA |
| Oh Dear ohdear.app | Monitoring Tools | Sending notifications and alerts | US |
| Panelfox panelfox.io | — | Inbound Emails | USA |
| Participant Kit consentkit.com | HR Tech | Email provider - Application emails (US alternative) | USA |
| Pinpoint pinpointhq.com | HR Tech | Email functionality | United States |
| Plain plain.com | AI/ML | Email processing | US |
| Proctorio proctorio.com | EdTech | Transactional email support provider | USA |
| Project.co project.co | Productivity | Transactional Email | USA |
| PropelAuth propelauth.com | Cybersecurity | Email management | United States |
| ProsperStack prosperstack.com | SaaS | Transactional email | United States |
| Pylon usepylon.com | Customer Support | Email Marketing | USA |
| Rally UXR rallyuxr.com | Research Operations | Email Service Provider | US |
| Recruit participants testable.org | EdTech | Self-hosted service for transactional emails | USA |
| Refersion refersion.com | Marketing | providing transactional email services on behalf of Refersion | Philadelphia, PA |
| Resgrid resgrid.com | Public Safety Technology | Email | USA |
| Roofai roofai.com | AI/ML, Real Estate Tech | Email Service Provider | USA |
| Routable routable.com | Fintech | Customer email delivery platform | Chicago, IL, USA |
| Schedulista schedulista.com | Productivity | Email provider. | Newtown, PA |
| Scribe-mail scribe-mail.com | Marketing | Transactional email | USA |
| SendBoard sendboard.com | Productivity | Email service | — |
| Smartlockr smartlockr.io | Cybersecurity | Email notifications | N/A |
| Social Card joinsocialcard.com | Marketing | Email Delivery | Not specified |
| Sprinto truthscan.com | AI Detection, Cybersecurity | Transactional email | — |
| Supercycle supercycle.com | E-commerce | Email communications | USA |
| Tackle tackle.io | Cloud GTM | Customer Email and Marketing Service | USA |
| Talkjs talkjs.com | Communication/Chat API | Sending email notifications | EU |
| TimeZest timezest.com | Productivity | Transaction Email Processing | United States |
| Tuple tuple.app | Productivity | Transactional application email | United States |
| Ubicloud ubicloud.com | Cloud Infrastructure | Email delivery platform | Global |
| Userflow userflow.com | Product Adoption | Transactional email service | USA |
| Userinterviews userinterviews.com | Research Technology | Sends transactional emails to Researchers and Participants | USA |
| WhisperAPI whisper-api.com | — | Transcription Notification Emails | US |
| WorkOS workos.com | DevOps | Email Delivery | United States |
| Worksome worksome.com | HR Tech | Email sending | US |
| Zeplin zeplin.io | Design Delivery Tool | Zeplin uses Postmark to provide email services, for transactional emails and for service notifications. Postmark infrastructure processes some Zeplin email traffic and provides some email security services. | United States |