Postmastery has published the tenth edition of its Email Delivery Benchmark, covering April to June 2026. It is drawn from 15.5 billion transactions sent by large ESPs and compares delivery, bounce and deferral rates at 15 mailbox providers
Comcast was the hardest provider to deliver to. It accepted 88.12% of mail sent to it, bounced 11.88% and deferred 52.05% of delivery attempts. The average message took an hour and 46 minutes to arrive. Mimecast came next from the bottom, accepting 93.74% with a deferral rate of 24.73%.
These figures measure what senders experienced. High deferral and bounce rates can reflect a provider’s filtering and the age of senders’ lists as much as the provider itself. Old comcast.net addresses bounce.
Seznam was at the other end. The Czech provider delivered 99.95%, and its median sender saw mail arrive in six seconds. Yahoo delivered 99.81% and deferred just 0.57% of attempts.
Google carries the most volume, 28.5% of the dataset. It delivered 97.66%, but deferred 15.34% of attempts. Outlook deferred 2.85% and Yahoo 0.57%. Of the three biggest providers, Gmail is the one most likely to tell you to try again later.
The report’s second table splits delivery time by sender quartile, and it shows why averages can mislead. Virgin Media has the slowest average delivery time in the report at an hour and 47 minutes. Its median sender waited three minutes and 17 seconds. A handful of senders stuck for close to ten hours dragged the average up. On the median, which Postmastery calls the more meaningful comparison, Orange is slowest at 25 minutes 52 seconds, followed by Comcast at 16 minutes 46 seconds.
One point to watch when quoting the numbers. Postmastery’s covering email says all the figures are medians. The report’s own notes say the headline table uses averages. Only the delivery-time breakdown gives medians.
Postmastery reports no notable or unusual SMTP responses in the quarter. The news pages at the back summarise Microsoft’s SNDS changes, progress on DKIM2, the publication of DMARCbis and the CNIL’s consent rules for tracking pixels in marketing email.
The figures describe mail from the senders in Postmastery’s dataset. They are a useful yardstick for anyone sending through a large ESP. They are no census of the whole market.
Postmastery is a Strategic Partner Member of emailexpert, supporting our mission to connect email and digital messaging professionals worldwide.
