One of the key features of the Sales Manager is the ability to email invoices back to head office. This uses a package called JavaMail, which has been ported from standard Java to Android. It allows mail to be sent via any SMTP server, not just the one used by Gmail.
Originally the Android client allowed the user to use any email account, when sending invoices. This meant that he had to specify the address of the SMTP server, but unfortunately most users do not know what this was. Mail services will usually tell you what the address of their POP3 server is, but this is not the same thing.
I got so many support requests about this that I decided to restrict the feature to Gmail accounts. The problem with this was that Google got very shirty about emails being sent autonomously. So I started to get support requests about this, and the error messages being returned by JavaMail did not help.
To resolve this, I plan to allow invoices to be sent from Outlook and Yahoo accounts, and possibly other mail services as well. But I doubt that I will return to the free for all that I allowed in the past.