Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
MailMate 1.5 for Mac App Review
Everyone uses email at some point. It has been integrated into everyday life so much it is more or less impossible to avoid it, which is why a decent email client is important to find, especially if your particular lifestyle requires heavy use of it. MailMate is designed for the serious email user who has a lot to send, a lot to receive and a lot to organise. There are no fancy graphics or anything like that here, just plain, boring windows of data to get the job done without messing around. It certainly isn’t here to have fun but it gets the job done. If this sounds like your kind of thing, MailMate 1.5 is available now for Mac for $30.
MailMate really doesn’t accept any kind of fancy enhancements and proudly imposes plain text as your only option. You can always use the open-source formatting language Markdown to format your emails if you know it but if you really need to do that then this probably isn’t the right software for you. What you get here is grey buttons and straightforward text. MailMate values functionality over visuals and is all the better for it. If you stay in line and focus on the job at hand, you will get on with it just fine and find yourself becoming highly productive with your emailing. It is however lenient enough to show you incoming HTML messages and if you are really lucky it will also display attached images and PDFs, provided you enable this function in the settings.
On the surface, MailMate does not look good at all and you could be forgiven for dismissing it but if you take the time to get used to it, you will find it has a lot to offer. First of all, it can import all your other IMAP accounts from all clients and bring them into one convenient place. It also has a generous number of tools to give you some much needed shortcuts for wading through all your messages more efficiently.
Where it really excels though is in the functions for searching and filtering emails. The search criteria for this is as good as unlimited as you are unlikely to need them all but you can choose to search for a message by addresses, names or even specific words contained in the message. You can even dig deeper and search by server domain and various other complicated criteria that will be familiar to those with experience in email server administration. There is also an extensive supply of categories to help you sort through your emails and group them appropriately and if you really want to you can look behind the scenes and gain access to various analytics about your emails.
Fortunately none of this is necessary but the option is there if you are more experienced in computing. MailMate works on all levels so even beginners should have no problem dealing with their emails, although they are probably better suited to something a bit more colourful. MailMate may be good but it really is for basic email use and little else.