Regardless of billing software, I have often gotten a call from clients complaining that when they send out bills some of the bills are not readable. Most of the time the issue is that the bill sent to the client is winmail.dat rather than PDF and therefore can’t be read.
If this happens to you, the problem is usually not the billing software but how Outlook is setup. Microsoft has an article that addresses the issue.
This was brought to my attention by a senior support rep at Timeslips. Hope it helps you to get your invoices emailed to clients more smoothly.