So what would the context-free grammar for an address list look like? Something like this:Īddress-list -> address ( delimiter address )* For example, it allows us to transform something we intuitively understand, like an address list, into something formal that a computer can parse. What is a formal grammar? Formal grammars (and specifically in our case a context-free grammar) are a set of rules that define the structure of a string. That why we wrote a parser that analyzes addresses, and determines if they are valid or not, based on a formal grammar. A recursive descent parser for syntax validationĮmail address syntax is fairly complex, enough to make a pure regular expression based approach cumbersome and unmaintainable (check out RFC 2822 and RFC 5322 about proper email format then this discussion on Stackoverflow if you need some convincing). Our validator service actually consists of five micro-services: 1. We know that is a valid MX host while is not.įurthermore, the validator is ESP specific, so we can go way beyond valid syntax checks, bring in specific requirement for Gmail vs. We’ve sent billions of emails and collected a lot of ESP data. Our goal is to build a realistic address validator for the types of addresses we see every day. Our goal is not to make a perfect address validator that can validate every single address that has ever been created. There are 3 main reasons we feel like we needed to build our own service. Why did we create an Email Verification API? The Internet runs on the Robustness principle, and because of that mail servers will accept addresses that do not conform standards, but are otherwise understandable. The definitions that do exist frequently conflict. There is no single definition of what is valid syntax, for an email address, and what is not. To call the Guardpost API, just use the publishable API Key in the My Account tab of your Mailgun account (the one with the “pub-key” prefix).Īddress validation is hard for multiple reasons:Įmail address syntax is fairly complex, complex enough that it is difficult to express with a regular expression while being readable and maintainable for developers. This is not intended to be a bulk mailing list cleaning service and we reserve the right to disable your account if we see it being used as such. Of course, you can use Mailgun to send the double opt-in email, as well. We suggest using Guardpost as part of your email collection form to reduce typos and false address submission in conjunction with a link emailed to the address to confirm the email is valid (double opt-in). If you want to get started right away, check out the API documentation, or a little sample jquery app, as an example of how to use Guardpost in a signup form. You’ll need a Mailgun account to use the service, but you don’t have to send your emails through Mailgun. We’re launching this as a free service that anyone collecting email through web forms can (and should!) use. So today, we’re releasing a project we affectionately called Guardpost, as our newest API, and are also pulling back the curtain to show exactly how we built it. We looked at the validation services available and weren’t satisfied with any of them, either for performance, accuracy or completeness reasons. We actually have been working on email validation ourselves for years (more on that below). Įmail validation is a hard problem that every single developer, building anything on the web, has to deal with. For the latest on validations, check out this post. Disclaimer: We’ve added new features and adjusted the pricing of our email verifications.
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