RFC 2821 (Simple Mail Transfer Protocol), 4.5.3.1 Size limits and minimums :
message content
The maximum total length of a message content (including any
message headers as well as the message body) MUST BE at least 64K
octets. Since the introduction of Internet standards for
multimedia mail [12], message lengths on the Internet have grown
dramatically, and message size restrictions should be avoided if
at all possible. SMTP server systems that must impose
restrictions SHOULD implement the "SIZE" service extension [18],
and SMTP client systems that will send large messages SHOULD
utilize it when possible.
Het zou dus mogelijk kunnen zijn dat een mail met headers die totaal meer dan 64KB is, wordt geweigerd. Maar vziw gebeurt dat tegenwoordig idd vrijwel nooit meer.
recipients buffer
The minimum total number of recipients that must be buffered is
100 recipients. Rejection of messages (for excessive recipients)
with fewer than 100 RCPT commands is a violation of this
specification. The general principle that relaying SMTP servers
MUST NOT, and delivery SMTP servers SHOULD NOT, perform validation
tests on message headers suggests that rejecting a message based
on the total number of recipients shown in header fields is to be
discouraged. A server which imposes a limit on the number of
recipients MUST behave in an orderly fashion, such as to reject
additional addresses over its limit rather than silently
discarding addresses previously accepted. A client that needs to
deliver a message containing over 100 RCPT commands SHOULD be
prepared to transmit in 100-recipient "chunks" if the server
declines to accept more than 100 recipients in a single message.
Dus, als je geen Error 452 of 552 krijgt, kan je er vanuit gaan dat je mail goed aankomt.