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
Security Measures for Dealing with Commercial E-mails
Currently Internet frauds are quite widespread. Probably you have already received some e-mails from different type of lotteries with congratulations to you as lucky winner who should pay few hundreds of dollars for receiving few millions, or some other cute letters, for example, from your friends asking to make an urgent money transfer. These issues become even more serious after Epsilon e-mail database breach: Web scabs currently own enough information to fake out millions of users.
Therefore the main security rules should be learnt by each and every e-mail user. First of all you should never share sensitive financial information like PIN-codes, user-names, account numbers, credit cards credentials with unknown recipients. Remember that official representatives of reliable companies you probably work with do not practice sharing of this type of data by e-mail.
Do not ever open attachments in such e-mail and please escape clicking the links provided in the text of the message. Also you should not copy such links and paste it in your browser address line. Remember that bad guys are good in what they are doing and know many evil tricks to steal your financial data and even use your credit cards for their own purposes.
Install reliable antivirus software in case if you will receive some malware tool in the e-mails.
Scammers usually use non-USA IP addresses so it is reasonable to check it. In the Mac mailing software you need to choose “View”, afterwards go to “Message”, then check “Long Headers”, where you should examine “Received” folder to find out from which region the email was sent. Nevertheless please keep in mind that modern technologies for changing IP-locations are quite widespread and easy to use even for a school-child.
If the e-mail seems to be quite reliable for example presenting some special offers or discounts in the same manner as your product manufacturer or business partner usually do, please, spend few minutes and go to their official sites typing the address manually and check if the same offer or request is presented their. If there is no such information contact the hot-line and ask operators if such e-mails are valid and reliable. Doing in such manner you will inform your partners about possible acts of skin-games with the usage of their brand name.