An unusual thing has happened yesterday (5 March 2016) to me after sending several short messages, each to 2 or 3 recipients. Each message contained an URL (http://www.money.pl/500zl/warszawa/), which belongs to a trusted Polish company. Probably, because of the phrase "money.pl" contained in the message body, Google/Gmail rejected all my messages. Then, I tried to resend all of the messages. The outcome was the same. Finally, I modified each message by removing the URL from the message body and then I sent my modified messages to all intended recipients successfully. However, after that, when I wanted to send some other messages to several people (including myself), all the messages were not sent and Google/Gmail displayed the following error message: "An Outgoing server (SMTP) error occurred while sending mail. The server responded: 5.4.5 Daily user sending quota exceeded. v140sm1406383Ifd.24 - gsmtp." I have never before seen such an error message on my (the same) computer and am totally surprised how come the above situation occurred. I contacted my local ISP and he confirmed that there was nothing to be blamed on him. He suggested that I write to Google support but, as you know, this is not straightforward and easy. However, I did submit the description of my brand-new problem in an online form available at https://support.google.com/mail/answer/22839?hl=en. Nothing, so far, has changed and no response from Google has been received (I provided my two e-mail addresses). Can anybody experienced enough clarify this unusual irritating problem and suggest how to restore the normalcy to my Gmail free private account. Because of the above-described mishap, I had to use Windows Live Mail and my Yahoo! account to retain the continuity of my replying and sending new messages using my local e-mail client (Thunderbird 38.6.0) that connects to my Gmail account. I'm now even not allowed to send e-mails directly from my online Gmail account. I would also welcome a solid explanation as to what actually happened yesterday to my Gmail account and why. I wish to reiterate: nothing like this has ever before happened to my Gmail account. FYI, I use a desktop PC with Windows 10 Pro 64-bit OEM with all latest updates to both the O/S and numerous protection applications installed.