Does the tool support custom metadata?

Yes, Explorer supports custom metadata (and Content Types).

The user can map source Content Types to target Content Types and specify values for custom metadata fields prior to uploading.

SLIM Companion Explorer supports the following column types:

• Single line of text
• Multiple lines of text
• Choice
• Number
• Currency
• Date and Time
• Yes/No
• Person or Group
• Hyperlink or Picture
• Managed metadata
• Lookup
• Enterprise Keywords (only read)
• Location

Email metadata like To, From, Subject, Conversation, ... is automatically extracted from eml and msg files and captured into SharePoint / OneDrive for Business columns. Extracting properties from commonly used file formats such as PDF, Office formats and image formats is also supported.