2.2.1 [RFC5545] Section 3.1, Content Lines


The specification states that content lines are delimited by a CRLF sequence.

Microsoft Office Outlook 2007, Microsoft Outlook 2010, Microsoft Outlook 2013, Microsoft Outlook 2016, Microsoft Outlook 2019 

On import, Outlook can parse files that use any combination of CRLF, CR, or LF as content line delimiters. On export, Outlook uses CRLF as the content line delimiter.


The specification states, "Lines of text SHOULD NOT be longer than 75 octets, excluding the line break. Long content lines SHOULD be split into a multiple line representations using a line 'folding' technique."

Office Outlook 2007, Outlook 2010, Outlook 2013, Outlook 2016, Outlook 2019  

On export, Outlook uses a CRLF followed by an HTAB character to fold lines and ensure no line is longer than 75 octets, as recommended. On import, Outlook parses any line regardless of length, and treats any of the following as a line fold: CR followed by SPACE or HTAB, LF followed by SPACE or HTAB, and CRLF followed by SPACE or HTAB.


The specification uses Augmented Backus-Naur Form (ABNF) to define the format of content lines.

Office Outlook 2007, Outlook 2010, Outlook 2013, Outlook 2016, Outlook 2019  

On import and export, Outlook conforms to the ABNF rules specified. On import, Outlook attempts to salvage any content lines that do not conform to the ABNF rules in some scenarios, but in general ignores any lines that do not conform. Additionally, the following hexadecimal encodings are ignored on both import and export:

U+0000, U+0001, U+0002, U+0003, U+0004, U+0005, U+0006, U+0007, U+0008, U+000B, U+000C, U+000E, U+000F, U+0010, U+0011, U+0012, U+0013, U+0014, U+0015, U+0016, U+0017, U+0018, U+0019, U+001A, U+001B, U+001C, U+001D, U+001E, U+001F, U+007F, and U+FEFF (Note: in UTF-8, the U+FEFF character is encoded as three octets: 0xEF, 0xBB, 0xBF.)