Technical

Trekkie Monster. He’s obsessed by social media and isn’t owned by Children’s Television Workshop. What is a Cookie? I’m not talking about biscuits, nor about web cookies, at least not exactly. When you’re talking to a protocol developer a cookie is a thing you’re given, that you hang on to for a while, then give back. If you leave your suitcase with your hotel concierge they’ll give you a paper ticket with a number on it. That ticket and the number on it aren’t of any intrinsic value, nor do they really mean anything. The only thing you can do with it is give it back to the concierge to get your suitcase back. The ticket is a cookie. Conceptually a cookie isn’t something that’s meaningful except when you give it back to whoever gave it to you – so if you’re a client program and a server sends you

Read about what a webhook is, how it can be used with your apps, and how to get started using webhook APIs. The post What’s a Webhook? appeared first on SendGrid.

Seen this recently? 451 Message temporarily deferred due to unresolvable RFC.5321 from domain; see https://postmaster.yahooinc.com/error-codes This is Yahoo doing some extra work to identify that the 5321.From domain1 of the mail is acceptable to them. Yahoo are going (slightly) beyond what’s required for the return path to be valid in SMTP terms. SMTP just requires that the return path be syntactically valid – i.e., looks like an email address – and that it be deliverable. The basic DNS check you might do would be to check if the right-hand-side of the email address has an MX record2. So for a bounce address of bounces@email.example.com you’d check to see if email.example.com had an MX record. Yahoo want to also check that it looks like a legitimate address in another way, that the organizational domain of the right-hand-side looks legitimate. The organizational domain is what you might think of as a “domain”

Learn about the differences between ports 465 and 587, why there’s so much confusion around the ports, and how to best use these ports. The post SMPT Port 465 and Port 587: What’s the Difference? appeared first on SendGrid.

Use these 5 steps to authenticate your email program. Authentication will help mailbox providers recognize you as a legitimate sender and protect you from phishing. The post How to Authenticate Your Email in 5 Steps (Email Authentication 101) appeared first on SendGrid.

Several times recently I’ve heard about something unusual happening email delivery-wise at academic domains that was new, and wasn’t being seen at non-academic domains on the same lists. Most recently it was aggressive following of all links in an email at delivery time, seen at several .edu domains, all using the same mail provider. Not that unusual a thing in itself, we know that corporate malware filters have done this for a while. But this seemed more aggressive than just “this mail looks iffy, lets sample a few links and look for malware”, and the new behaviour was only being seen on .edu recipient domains, not on any of the non-academic domains using the same mail provider. If any .edu postmasters can explain, please, do, but my speculation is that one big difference between academia and the corporate environment is how much control the IT security folks have over recipient

New to the email queue? We’ve got you covered. This tutorial will show you how how to view, flush, and purge queued mail in Postfix. The post How to Flush the Mail Queue in Postfix appeared first on SendGrid.

Return-path is a hidden email header that indicates where and how bounced emails will be processed and is used for collecting and processing bounced messages. The post What Is Return-Path Header (And Why It Matters) appeared first on SendGrid.

When we’re looking at the technical details of email addresses there are two quite different contexts we talk about. One is an “821 address” or “5321 address”. This is the email address as it’s used by the SMTP protocol, as part of the “MAIL FROM: ” or “RCPT TO: ” commands sent to the mailserver. It’s defined in RFC 821, now updated by RFC 5321, hence the name. If someone mentions the “envelope” or they’re talking about “bounce addresses”, this is the sort they mean. We’re not talking about them in this post. The other is an “822 address” or a “5322 address’. They’re the ones the recipient sees in the To: or From: headers. They’re named after their RFC, RFC 5322. This is the sort of email address most folks mean by default, unless they’re explicitly talking about the envelope of an email, but if someone describes an email

It looks like Microsoft are getting pickier about email address syntax, rejecting mail that uses illegal address formats. That might be what’s causing that “550 5.6.0 CAT.InvalidContent.Exception: DataSourceOperationException, proxyAddress: prefix not supported – ; cannot handle content of message” rejection. Why do we care? It’s good to send syntactically valid email in a warm fuzzies sort of way – it shows we know what we’re doing, and aren’t dodgy spamware – but it’s increasingly important to delivery as mailbox providers are tightening up on their syntax checks. But why are mailbox providers doing that? One reason is that authentication tech like DKIM and DMARC is built around them only being applied to email. Not to messages that kinda look like email. There are ways to bypass DKIM protections by sending invalid messages. As one example, if you send multiple copies of the From: header with different values a DKIM checker