@Brittney They do.  :)  I believe there are some limitations around size and type, but otherwise, yes.

@heather_hansen thank you for the quick response! Do you know where I could find information on the limitations around size and type by chance? And do the attachments sync automatically or are there specific steps the CSMs need to take to make sure an attachement syncs successfully to the timeline activity? Thanks!

@Brittney found this in some documentation.

The following are the attachment file types that are supported: jpg, jpeg, gif, png, bmp, pdf, doc, docx, txt, ppt, pptx, xls, xlsx, and csv.

And then, this has some additional limitations:

https://support.gainsight.com/SFDC_Edition/Timeline/Admin_Guides/Configure_Email_to_Timeline#Limitations

@heather_hansen thank you so much for your help and sharing!

@heather_hansen Thank you for the quick help!