Microsoft recently announced that Exchange Online -- the email (and calendar, contacts and tasks) functionality provided in Microsoft 365 and Office 365, will be subject to outbound email rate limits as of January 2025. That "external recipient rate limit" will be 2,000 recipients every twenty-four hours. Though the note on limits suggests that users needing to send larger volumes of mail might want to consider Azure Communication Services for Email, another article covers options for High Volume Email Sending for Microsoft 365. The high volume option still seems to have limits -- 100,000 ex ..read more

Tony Patti has worked in the email sphere for more than twenty years. An expert deliverability consultant (and builder/manager of deliverability service consulting as a practice), he’s somebody I could on some level consider a competitor. We’ve worked for different companies and on different email platforms over the years, but with similar goals: Helping clients get their mail successfully delivered to the inbox by teaching them how not to be a spammer. You can find his Linkedin profile here. Tony, thank you for taking the time to talk to me today! Your career path is an interesting one. H ..read more

Have you ever seen this SMTP error message? 450 4.2.1 The user you are trying to contact is receiving mail at a rate that prevents additional messages from being delivered. Please resend your message at a later time. If the user is able to receive mail at that time, your message will be delivered. For more information, go to Limits for sending & getting mail. I certainly have! And somebody just reached out to me after running into it themselves. I’ve blogged about it before, but I thought it would be useful to address it again, with a bit more detail and clear links through to resoluti ..read more

Who hosts what mail? MBP Spotlight is the new series here at Spam Resource where I’ll share ranking data for the top mailbox providers (including B2B!) based on where they fall in the top ten million domains. Some entries might have more info, some entries might have less, depending on what information I know about them and what information I can find online. To count rankings, I took a snapshot of MX records for the top ten million domains, and then rolled them up based on the domain name hosting mail for each domain. That shows me how many domains have their inbound email hosted by hosted ..read more

Hey, look what I stumbled across! Chris Zullo, Salesforce Consultant and Business Puzzle Solver, did a most excellent job capturing my 2020 presentation on deliverability for Salesforce Marketing Cloud, talking about best practices, domain and IP strategy recommendations, what features you need to implement domains in various different scenarios, how to send as the top level of a domain from Marketing Cloud, how Sender Authentication Package brands all the domain touchpoints in your email sends, and more. It's from May 2020, but though a few years old, the fundamentals here are still qu ..read more

Publisher's note: I asked Mike Hillyer, co-founder of Kumo Corp, the folks behind the new open source high-performance MTA platform KumoMTA, if he might want some blog space to talk about KumoMTA and how it can help folks handle modern MTA-level deliverability challenges. I think the topic he chose, domain-related mailbox provider 4xx deferrals and how to handle these, is well appropriate in this modern age where Gmail and Yahoo Mail deferrals are way up for various folks, for various reasons, all ultimately related to the new Google and Yahoo sender requirement updates. Take it away, Mike ..read more

Are you tying to send mail to users at Microsoft OLC domains like Outlook.com and are receiving rejections back that look like this: 532 5.3.2 STOREDRV.Deliver; Missing or bad mailbox Database property If so, know that you are not alone. Microsoft seems to be rejecting some percentage of mail right know with this unique 5.3.2 error code. Talking to various email service provider (ESP) platforms, there is a lot of mail being rejected with this error message, but nowhere near 100% of mail. So you might be seeing lots of these rejections, or very few. Hard to say; in my tiny email universe it's ..read more

Sree writes: Help! Our newsletter business is receiving the Gmail "unusual rate of unsolicited mail mentioning your URL" error message. Specifically: "421 4.7.28 Gmail has detected an unusual rate of unsolicited mail containing one of your URL domains. To protect our users from spam, mail with the URL has been temporarily rate limited. " "This seems to go away if we send really slowly, but that is far from optimal, as we’re not able to send to our entire subscriber database. What could we be doing wrong? How do we fix this?" This can be a tricky one to figure out because it’s hard to know ..read more

WOW! Thank you everyone for your readership, friendship, shared knowledge and insight over the years. Thanks to your partnership and participation, Spam Resource has just reached 4 million views, according to my blog stats! (4,000,231 as of the morning of Sunday, April 7th.) Spam Resource launched in 2001, initially self-hosted with hand-edited HTML files. In 2006, I moved everything to Google's Blogger platform, where this thing has been hosted since. Blogger, incidentally, did not implement its own view tracking until mid-2010. Thus, 4 million views since, basically, July 31, 20 ..read more

First in a new series: Who hosts what mail? MBP Spotlight is the brand new series here at Spam Resource where I’ll share ranking data for the top mailbox providers (including B2B!) based on where they fall in the top ten million domains. Some entries might have more info, some entries might have less, depending on what information I know about them and what information I can find online. To count rankings, I took a snapshot of MX records for the top ten million domains, and then rolled them up based on the domain name hosting mail for each domain. That shows me how many domains have their i ..read more