I failed to receive three emails last night that were sent to me from people using gmail accounts.
The headers arrived, but the text on each was shown blank, and as 0.00B long.
I was able to receive a forth message that I sent as a plain text message.
The headers from the one of the non-plain-text messages that I was not able to view showed it as having:
Content-Type: multipart/alternative; boundary=047d7b6226d0067f1304df065754
The other two non-plain-text messages also showed as multipart/alternative, but different "boundary" codes. (Both codes starting with 047d7b, as it happens.)
I'm using IMAP to connect to my email server.
I'm able to use Thunderbird to connect to my email server with IMAP and successfully read all three emails.
I'm successfully received some different multipart/alternative emails recently using AquaMail; these emails were sent from non-gmail accounts.