Email syntax

An email address has two parts separated by @: the local part (the mailbox name, like jane.doe) and the domain (like acme.com). RFC 5322 defines the grammar, called addr-spec. The usual dot-atom form allows letters, digits, dots and a set of symbols in the local part (including + - _ and less common ones such as ! # $ %), with dots not allowed at the start or end or twice in a row. The standard also permits rarer forms like quoted local parts, which many mail systems refuse in practice.

RFC 5321 adds length limits: the local part can be at most 64 octets, and the whole forward path at most 256 octets including the angle brackets, which leaves 254 characters for the address itself. Internationalized addresses with non-ASCII characters are allowed by the SMTPUTF8 extension (RFC 6531), but only if every server on the path supports it.

The local part is technically case-sensitive under the standard, though nearly all real mail servers treat it as case-insensitive. Plus addressing ([email protected]) is valid syntax and widely supported, but how the suffix is handled is up to each provider.

Syntax errors are the cheapest problem to catch: a missing dot, a comma instead of a period, a trailing space from a spreadsheet. Sending to a malformed address fails immediately. But correct syntax only means the address could exist, not that it does, so a syntax check is the first step of email verification, not a replacement for it.

Skrap.ai checks syntax first on every address, then the domain and MX records, then the mailbox over SMTP. A malformed address comes back Invalid, and Invalid results don't cost a credit. Bulk CSV uploads show the estimated credit cost before processing, so you can clean a messy export with the free email verifier or a paid plan.