reminders

when can I send reminders, how often are they sent...
some Q's about that...
th

and why are they so big?
And why not just text?
I know of folk who deliberately filter out all email that isn't plain text as it is almost always spam.

there is nothing about them in the help section.
are they always sent to my opponent, when I click on the icon?
after how many days do they apear? and when do they come back?
th