Message being rejected due to size limit - how do I increase maximum size?

I have my ISP email forwarded to a Gmail account and then forwarded to my Exchange account.  I have an email sitting in the Gmail account that has 4 attachments, totalling 21095KB.    I can't for the life of me get it to transfer to my Exchange server.  I keep making changes to Exchange and then re-forwarding the message, but every time I get the following message:

Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 552 552 5.3.4 Message size exceeds fixed maximum message size (state 18).

I have searched and searched for the answer to this issue.  I modified the max message size send and receive connectors on my Exchange server and set it to 25600KB (25MB).  I also modified the global settings to that same capacity.  Here is the readout of Get-ReceiveConnector:

Identity                                MaxHeaderSize                           MaxMessageSize
--------                                -------------                           --------------
DGX\Default DGX                         128 KB (131,072 bytes)                  25 MB (26,214,400 bytes)
DGX\Client DGX                          128 KB (131,072 bytes)                  25 MB (26,214,400 bytes)

Here is the readout of Get-TransportConfig:

MaxReceiveSize : 25 MB (26,214,400 bytes)
MaxSendSize    : 25 MB (26,214,400 bytes)

I've also verified that my user account does not have a specific message size limit imposed on it.

I have tried restarting the Transport service in addition to restarting the whole server multiple times after adjusting various values.  What must I do to allow up to 25MB of attachments?