2.2.54 [RFC5545] Section 3.8.1.1, Attachment

V0088:

The specification states that the default value type for the ATTACH property is URI, and that the value type can be set to BINARY to indicate inline binary encoded content information.

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

On import, Outlook imports all binary attachments that have a value type of BINARY and are encoded with base64 encoding. All cid: URIs are ignored. All invalid and non-cid: URIs are imported as .url file attachments.

V0089:

The specification states that non-standard, inline encoding, format type and value data type property parameters can be specified on the ATTACH property.

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

On export, Outlook exports the VALUE, ENCODING, and X-FILENAME parameters on the ATTACH property. For more details, see [MS-OXCICAL] sections 2.1.3.1.1.20.1, 2.1.3.1.1.20.1.3, and 2.1.3.1.1.20.1.4.

On import, if the ATTACH property has a VALUE parameter set to BINARY and an ENCODING parameter set to BASE64, then the attachment is imported as binary data. If the ATTACH property has no ENCODING parameter and does not have a VALUE parameter set to BINARY, the attachment is imported as URI data. ATTACH properties that do not match these two scenarios are ignored. If any X-FILENAME parameters are present, then only the first instance is used in the user interface ([MS-OXCICAL] section 2.1.3.1.1.20.1.4). Any other parameters are ignored.

V0090:

The specification states that the ATTACH property can be specified within the VEVENT, VTODO, VJOURNAL, or VALARM components.

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

Outlook only exports the ATTACH property within VEVENT components. On import, ATTACH properties in any component other than a VEVENT component are ignored.

C0015:

The specification uses ABNF notation to describe the format of the ATTACH property. The ABNF shows a particular order for the parameters, but it is unclear whether this order is required.

 attach      = "ATTACH" attachparam ( ":" uri ) /
               (
                 ";" "ENCODING" "=" "BASE64"
                 ";" "VALUE" "=" "BINARY"
                 ":" binary
               )
               CRLF
  
 attachparam = *(
             ;
             ; The following is OPTIONAL for a URI value,
             ; RECOMMENDED for a BINARY value,
             ; and MUST NOT occur more than once.
             ;
             (";" fmttypeparam) /
             ;
             ; The following is OPTIONAL,
             ; and MAY occur more than once.
             ;
             (";" other-param)
             ;
             )

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

On export, Outlook orders the parameters for the ATTACH property differently than shown in this ABNF notation.

On import, Outlook can parse the parameters for the ATTACH property regardless of order.