A colleague has created a Bookings page for clients both internal and external to our organisation. The logo they have chosen appears fine in the confirmation e-mail sent to an internal client. (Outlook 365 on Windows 10.) However, when the confirmation e-mail is received by an external client, the logo is not displayed in the e-mail. Instead it is replaced by the text "[Logo]". The logo as well as the 'invite.ics' are sent as attachments. (External devices tested so far include: Gmail app on Android, Gmail web page on Chrome (Windows 10) & Outlook 365 on Windows 10.) I created a test site and found exactly the same issue.
Is this expected behaviour? Is it a known issue with the e-mail formatting?
I have found it surprisingly hard to find anything on this exact issue. The closest I have found is this -