3.4.2. WHITE SPACE

Note: In structured field bodies, multiple linear space ASCII characters (namely HTABs and SPACEs) are treated as single spaces and may freely surround any symbol. In all header fields, the only place in which at least one LWSP-char is REQUIRED is at the beginning of continuation lines in a folded field.

When passing text to processes that do not interpret text according to this standard (e.g., mail protocol servers), then NO linear-white-space characters should occur between a period (".") or at-sign ("@") and a <word>. Exactly ONE SPACE should be used in place of arbitrary linear-white-space and comment sequences.

Note: Within systems conforming to this standard, wherever a member of the list of delimiters is allowed, LWSP-chars may also occur before and/or after it.

Writers of mail-sending (i.e., header-generating) programs should realize that there is no network-wide definition of the effect of ASCII HT (horizontal-tab) characters on the appearance of text at another network host; therefore, the use of tabs in message headers, though permitted, is discouraged.