Hi Everyone,
I can confirm that the Modern EAC as the same problem as the older version pointed out by Fred74270 back in 2020. The workaround is slightly different but pretty much the same in operation.
I suspect the reason for this is the recipient limit is now a global setting and cannot be set per mailbox anymore. This is annoying and a security hole a mile wide The_Exchange_Team please take note: I would much rather have specific accounts e.g. sales or marketing or HR set to the larger limit and everyone else shut down to a handful of recipients in case they get compromised. As it stands now I am having to toggle this back to the lower limit after the higher one has been used for a mass mailing.
New version workaround as follows. The three dots menu has been removed from the Modern EAC. Selecting all accounts with the first tick box adds a new button "Recipient Limit" to the top row. This will open a dialog box which allows the setting of a recpient limit globally. Mine was blank so I am assuming the global default is 100.