There are several objects that have required minimum maximum sizes. That is, every implementation must be able to receive objects of at least these sizes, but must not send objects larger than these sizes.
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* *
* TO THE MAXIMUM EXTENT POSSIBLE, IMPLEMENTATION *
* TECHNIQUES WHICH IMPOSE NO LIMITS ON THE LENGTH *
* OF THESE OBJECTS SHOULD BE USED. *
* *
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The maximum total length of a user name is 64 characters.
The maximum total length of a domain name or number is 64 characters.
The maximum total length of a reverse-path or forward-path is 256 characters (including the punctuation and element separators).
The maximum total length of a command line including the command word and the <CRLF> is 512 characters.
The maximum total length of a reply line including the reply code and the <CRLF> is 512 characters.
The maximum total length of a text line including the <CRLF> is 1000 characters (but not counting the leading dot duplicated for transparency).
The maximum total number of recipients that must be buffered is 100 recipients.
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* *
* TO THE MAXIMUM EXTENT POSSIBLE, IMPLEMENTATION *
* TECHNIQUES WHICH IMPOSE NO LIMITS ON THE LENGTH *
* OF THESE OBJECTS SHOULD BE USED. *
* *
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Errors due to exceeding these limits may be reported by using the reply codes, for example:
500 Line too long.
501 Path too long
552 Too many recipients.
552 Too much mail data.