Daily limit exceeded
Which daily limit are you asking about?
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I can only think of one reason for a daily limit imposed by eM Client, and that is when using a Free License there is a limit in the number of translations you can do each day.
There could also be limits imposed by your server for the number of emails you can send in one day, or the total size of emails you can send in one day.
If it shows up again, make a note of the exact error, or take a screen shot, and somebody will be able to clarify what it is.