Mimecast provides “cloud cybersecurity services for email, data and web,” specializing in cloud-based email management for Microsoft Exchange and Microsoft Office 365, including security, archiving, and continuity services to protect business mail.
To clients and users, Mimecast may seem like an integrated Microsoft add-on, but from a sender’s perspective, Mimecast is effectively its own mailbox provider. Typical Mimecast customers point their domains’ MX records at Mimecast infrastructure and any inbound mail is rejected or accepted by that infrastructure before being logged, processed, archived (if archiving is enabled), before being forwarded to the actual end user mailbox for the email message’s destination.
Mimecast hosts inbound email services for many thousands of email domains. When cross-referenced against the top 10 million domains, Mimecast shows up in the MX record for over 37,000 of those domains. While this is smaller than Google (~800,000) and Microsoft (~727,000), a lot of the entities you’ll see utilizing Mimecast for email security and routing are heavy hitters – known brands, Fortune 500 companies, and big players in various industries. As of November 2023, companies that utilize Mimecast include Forbes, HP, USA Today, Gannett, Aetna, Anheuser Busch, Cleveland Clinic, the NFL, and Sanofi.
For senders finding themselves blocked by Mimecast, they do operate an unblock request form (https://community.mimecast.com/s/sender-feedback) but are quick to caution that senders are likely to have the best chance at addressing a blocking issue by working directly with the B2B enterprise client who has chosen to implement Mimecast security and filtering, as those users are able to create and manage whitelist/allowlists and blocklists at the sender level, via “Permitted Senders Policy” settings in the Mimecast administration console.
There you’ll find information regarding the limit of concurrent SMTP connections (20), limits of recipients per DATA (100), when a 4xx deferral denotes greylisting, and more. Keep in mind, as noted above, Mimecast administrators (i.e. customers of Mimecast) may choose to block some senders, IP addresses, or domains, so that even though you're blocked by Company X, and Company X uses Mimecast for inbound email handling and email security, it doesn’t mean that Mimecast themselves have instituted a block against you.
The top 25 email domains (ranked slightly non-scientifically, based on website traffic, not email traffic) hosted by Mimecast are:
penguinrandomhouse.com
forbes.com
steamcommunity.com
ultipro.com
bkstr.com
hp.com
hubspot.com
betfair.com
teamviewer.com
usatoday.com
audacy.com
aetna.com
surveymonkey.com
disqus.com
coldwellbankerhomes.com
pokemon.com
lionsgate.com
newsmax.com
tandfonline.com
toasttab.com
flipkart.com
fanatics.com
cambridge.org
optimizely.com
redhat.com
Note: A common question I get is, why do I rank domains against website traffic rankings instead of based on email data? It’s because I don’t have the right level of granular email data available to me to put similar rankings together based on email-related criteria. While this makes email rankings slightly imperfect, I think it still provides a “good enough” methodology to provide insight into how big or how well-known various domains (and their companies) are.
Mimecast provides “cloud cybersecurity services for email, data and web,” specializing in cloud-based email management for Microsoft Exchange and Microsoft Office 365, including security, archiving, and continuity services to protect business mail.
To clients and users, Mimecast may seem like an integrated Microsoft add-on, but from a sender’s perspective, Mimecast is effectively its own mailbox provider. Typical Mimecast customers point their domains’ MX records at Mimecast infrastructure and any inbound mail is rejected or accepted by that infrastructure before being logged, processed, archived (if archiving is enabled), before being forwarded to the actual end user mailbox for the email message’s destination.
Mimecast hosts inbound email services for many thousands of email domains. When cross-referenced against the top 10 million domains, Mimecast shows up in the MX record for over 37,000 of those domains. While this is smaller than Google (~800,000) and Microsoft (~727,000), a lot of the entities you’ll see utilizing Mimecast for email security and routing are heavy hitters – known brands, Fortune 500 companies, and big players in various industries. As of November 2023, companies that utilize Mimecast include Forbes, HP, USA Today, Gannett, Aetna, Anheuser Busch, Cleveland Clinic, the NFL, and Sanofi.
For senders finding themselves blocked by Mimecast, they do operate an unblock request form (https://community.mimecast.com/s/sender-feedback) but are quick to caution that senders are likely to have the best chance at addressing a blocking issue by working directly with the B2B enterprise client who has chosen to implement Mimecast security and filtering, as those users are able to create and manage whitelist/allowlists and blocklists at the sender level, via “Permitted Senders Policy” settings in the Mimecast administration console.
Mimecast publishes detailed information regarding 4xx and 5xx SMTP deferrals and rejections. Find that information here: https://community.mimecast.com/s/article/email-security-cloud-gateway-mimecast-smtp-error-codes
There you’ll find information regarding the limit of concurrent SMTP connections (20), limits of recipients per DATA (100), when a 4xx deferral denotes greylisting, and more. Keep in mind, as noted above, Mimecast administrators (i.e. customers of Mimecast) may choose to block some senders, IP addresses, or domains, so that even though you're blocked by Company X, and Company X uses Mimecast for inbound email handling and email security, it doesn’t mean that Mimecast themselves have instituted a block against you.
The top 25 email domains (ranked slightly non-scientifically, based on website traffic, not email traffic) hosted by Mimecast are:
Note: A common question I get is, why do I rank domains against website traffic rankings instead of based on email data? It’s because I don’t have the right level of granular email data available to me to put similar rankings together based on email-related criteria. While this makes email rankings slightly imperfect, I think it still provides a “good enough” methodology to provide insight into how big or how well-known various domains (and their companies) are.
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