when I set *.my.com it told me there is must a letter or number ,but if use letter or number I will can't set wildcard DNS, HOW CAN I DO IT
You can't set a wildcard DNS in the control panel, it is rumored you can ask Dreamhost to setup the DNS for you, but only if you have a worthy reason for using a wildcard DNS.
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Shonky is right. I can verify that if you do have a valid reason, they will have no problem in setting up a wildcard DNS entry for you!
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