We ranked 14 transactional email APIs by real-world reliability over the last 90 days, using 107 status page incidents and our own around-the-clock uptime checks. Transactional email carries password resets, sign-up confirmations, receipts and shipping notices, so when the sending API fails or queues back up, customers cannot log in or never get their order confirmation. A few hours of delayed or bounced mail turns into support tickets, abandoned sign-ups and duplicate orders, and messages that bounce during an outage are often never retried. Most small businesses send this mail through one provider's API, which makes that provider's delivery history worth checking.
Most reliable transactional email API:Mailjet (score 99.6/100). Highest uptime: Mailjet (100%). Fewest incidents: Mailjet (1 in 90 days). Fastest to resolve: Mailtrap Email Sending (avg 6m).
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Vendor
Score
Uptime (90d)
Incidents
Avg resolve
Transparency
Status now
1
MailjetMailjet is an email marketing and transactional email service owned by Sinch.
99.6
100%
1
—
100/100
Operational
2
Mailtrap Email SendingMailtrap is an email delivery platform with a sending API, SMTP relay and email testing sandbox, developed by Railsware.
98.2
99.99%
2
6m
100/100
Operational
3
LoopsLoops is an email platform for software companies that sends transactional, product and marketing email.
96.3
99.98%
1
1h 34m
100/100
Operational
4
Twilio SendGridTwilio SendGrid is an email delivery API and SMTP relay service owned by Twilio.
94.8
99.98%
5
1h 9m
100/100
Operational
5
SparkPost (Bird)SparkPost is an email delivery API and analytics service, now part of Bird (formerly MessageBird).
87.7
99.90%
8
2h
100/100
Operational
6
MailgunMailgun is an email sending API and SMTP service owned by Sinch.
83.2
99.84%
10 (3 major)
1h 43m
100/100
Operational
7
Elastic EmailElastic Email is an email delivery API and email marketing service based in Canada.
82.4
99.84%
3 (1 major)
6h 19m
100/100
Operational
8
BrevoBrevo, formerly Sendinblue, is an email marketing, SMS and transactional email platform headquartered in Paris.
70.5
99.68%
29 (5 major)
1h 24m
100/100
Operational
9
PostmarkPostmark is a transactional email delivery service from ActiveCampaign.
68.3
99.58%
8
7h 41m
100/100
Operational
10
ResendResend is an email sending API for developers, based in San Francisco.
60.5
99.39%
23 (4 major)
3h 39m
100/100
Operational
11
SMTP2GOSMTP2GO is an email delivery service offering SMTP relay and an HTTP API, based in New Zealand.
58.4
99.17%
17 (3 major)
5h 39m
100/100
Operational
Transactional Email APIs reliability at a glance
Across the 11 ranked transactional email APIs, average 90-day uptime is 99.76%. Reliability scores range from 99.6 (Mailjet) to 58.4 (SMTP2GO).
Together they published 107 incidents in the last 90 days, 16 of them partial or major outages.
The typical vendor takes 1h 51m to resolve an incident. Mailtrap Email Sending is fastest, at 6m on average.
Brevo reported the most incidents (29 in 90 days).
What to check before you choose a transactional email API
Look at incidents affecting the sending API, SMTP relay and outbound delivery first. Dashboard or analytics outages are an annoyance; delivery delays lock customers out.
Check whether the API queues and retries mail during an incident, and whether your own app retries on 4xx/5xx errors instead of dropping the message.
Watch for repeated delivery problems to Gmail or Microsoft inboxes, which show up as delays or bounces rather than full outages.
Keep a second provider configured for password resets and receipts if email is critical to your checkout or login.
90-day uptime history
Each bar is one day. Hover a bar for that day's uptime and incidents.
These vendors join the ranking once we have enough evidence: at least 14 days of data, and for vendors with a quiet status page (silent for a year, or for 90 days while their competitors report several incidents), 30 days of our own independent monitoring.
Amazon SES · quiet status page, awaiting our own monitoring
MailerSend · quiet status page, awaiting our own monitoring
What is the most reliable transactional email API?
Based on the last 90 days of data, Mailjet is the most reliable transactional email API we track, with a reliability score of 99.6/100 and 100% uptime.
How do you measure transactional email API reliability?
We poll each vendor's public status page every few minutes, record every incident, and run our own uptime checks against each vendor's login and customer-facing pages. Uptime (40%), incident frequency (20%), average time to resolve (20%) and transparency (20%) combine into one score out of 100.
How often are these rankings updated?
Continuously. Status pages and uptime checks run every five minutes and scores are recalculated several times an hour.
Can vendors pay to rank higher?
No. Sponsored placements are clearly labelled, shown separately from the rankings and never change a vendor's score.