ConstReadonlyaddressTooLong: "address-too-long"The complete address exceeds the 254-octet limit from RFC 5321.
ReadonlydomainEmpty: "domain-empty"The domain is empty, as in user@.
ReadonlydomainTooLong: "domain-too-long"The domain exceeds the 255-octet limit from RFC 5321.
ReadonlyinvalidAddress: "invalid-address"The input is not a single valid mailbox address.
ReadonlyinvalidDomain: "invalid-domain"The domain is not a valid DNS name or internationalized domain.
ReadonlyinvalidDomainLiteral: "invalid-domain-literal"The domain literal is not a valid IP address or general address literal.
ReadonlyinvalidHeaderValue: "invalid-header-value"A quoted string, comment, or display name contains a control character.
ReadonlyinvalidLineEnding: "invalid-line-ending"The input contains a bare line break or a fold without trailing whitespace.
ReadonlyinvalidLocalPart: "invalid-local-part"The local part is not valid dot-atom or quoted-string syntax.
ReadonlyinvalidUtf8: "invalid-utf8"The input contains an unpaired surrogate and is not valid UTF-8.
ReadonlylocalPartEmpty: "local-part-empty"The local part is empty, as in @example.com.
ReadonlylocalPartTooLong: "local-part-too-long"The local part exceeds the 64-octet limit from RFC 5321.
ReadonlymissingAt: "missing-at"The address has no @ separating the local part from the domain.
ReadonlyunsupportedCharset: "unsupported-charset"A display name uses an RFC 2047 character set that cannot be decoded.
The reason a mailbox address was rejected.
Each value corresponds to a distinct, programmatically recognizable failure, so callers can decide whether to retry, ask the user to fix the address, or drop it.