EWS Managed API 2.2 Read\Write extended properties of attachments - exchange-server

Question

Currently I'm working on migration of one big project from MAPI CDO to EWS (Managed API 2.2) to support Ex2016. All things were migrated well except one: I can't find the way how to read\write Attachments Extended Properties. Does anybody know how to do that or may be some workaround? This is very critical for me and I would be very appreciate for any help.
---Update:
Also tried to use native EWS to get property of attachment but without success too:
var ret = esb.GetAttachment(new GetAttachmentType()
{
AttachmentIds = new []{new AttachmentIdType()
{
Id = "AAMkADVhNjUzMzMyLTRiMDYtNDc4OS1hYjJjLWI1ZDA4ZWFhYTJkZQBGAAAAAADqFaOFYZSeQI5UObwGbjIJBwAOgaos6ORVS5+o5bQovn/kAAAAeN2cAAAOgaos6ORVS5+o5bQovn/kAAAeCoIuAAABEgAQAJPAuRg2gipPmEKfgW26mFU=",
}},
AttachmentShape = new AttachmentResponseShapeType()
{
BodyType = BodyTypeResponseType.Best,
BodyTypeSpecified = true,
IncludeMimeContent = false,
IncludeMimeContentSpecified = true,
AdditionalProperties = new []
{
new PathToExtendedFieldType() { PropertyType = MapiPropertyTypeType.Integer, PropertyTag = "0x3705"},
new PathToExtendedFieldType() { PropertyType = MapiPropertyTypeType.Integer, PropertyTag = "0x0E21"},
}
}
});
The response doesn't contain any of requested properties.
--- Update 2:
In project we use next properties of attachments:
PR_RECORD_KEY, PR_DISPLAY_NAME, PR_RENDERING_POSITION
PR_ATTACH_ENCODING, PR_ATTACH_NUM, PR_ATTACH_METHOD, PR_ATTACH_LONG_FILENAME, PR_ATTACHMENT_HIDDEN, PR_ATTACH_CONTENT_ID, PR_ATTACH_FLAGS, PR_ATTACH_MIME_TAG, PR_ATTACH_CONTENT_LOCATION, PR_ATTACH_SIZE
Also we create a couple of Custom Extended Properties with custom Property Set and tag some attachments with that props.
Some of Properties can be found in object model of EWS/ManagedApi like PR_ATTACH_SIZE but the problem with others and with custom props.
So we need to read/write standard attachment properties as well as custom.
In project we mark attachment itself, not embedded Item.

Answer 1

You can't access extended properties on Attachments or the Recipients collection in EWS outside of those properties that are made accessible as strongly typed properties by the API. The only place you can use Extended properties are at the message level.
That said can you explain more as to how your using Extended properties eg are these extended properties on embeded items. If that is the case then you could access those extended properties via the Item Attachment.
Looking at your code 0x3705 is the PR_ATTACH_METHOD property on an attachment there is no equivalent to this in EWS, rather EWS will return a different Attachment Class based on the Attachment type. Eg ItemAttachment, FileAttachment or ReferanceAttachment (eg for OneDrive Attachments). 0x0E21 is that Attachment number EWS is going to return the Attachments in the order of that number in GetItem request so you can compute that yourself. But the property is useless in EWS because to get an Attachment you need the EWSId unlike MAPI.
Cheers
Glen