New

Allow global email settings to be stored on a per company basis.

Whichever company data set my customer opens, if they go to Email Defaults the same email server settings are displayed, obviously these would then have to be applied to e.g. invoice layouts, but they might not see the folder containing the company invoice layouts that they wish to apply those settings to. Or are all the layout folders for the various company data sets accessible from the "Apply" email defaults button?

The user interface does not make it as obvious as it could, but the email client settings are global so if you edit the settings for SMTP or Microsoft Outlook these are stored centrally and not in the report itself. What is stored in the report is the specific email program selected as well as the specific email files and attachments settings. This means that you could have one report that uses SMTP and a different one that uses Microsoft Outlook, but the settings for those email clients would always be shared i.e. if you have 2 reports that specify the same email client they will use the exact same settings e.g. server, port, email, etc, regardless of if they are in the same company or different ones.

The customer specifically requires different email settings applied to invoice sent from each different company, so the send address, email login and password are all different. 

The only way that would be possible currently would be to have reports in one company set to use SMTP and the other to use Microsoft Outlook, and have the settings configured for each appropriately for the separate companies. Worth logging it as an idea to have support for per-company email client settings though.