If your mother was adopted do you automatically have to convert, or are there ever leniencies made? Especially if you grew up in an Ultra Orthodox Community?

A person is born Jewish if his or her mother was Jewish. If your mother was adopted, then whether or not you are Jewish depends on whether she was Jewish (which she might well have been, as Jewish children get adopted as well as non-Jewish ones). If she wasn't, then you (i.e. the "you" in your question) are not Jewish.

I suppose an adopted mother is the worse thing you could have in Judaism. Or maybe they don't exist.

What if you didn't know whether or not she was Jewish.
Do they ever give her the benefit of the doubt and rule favorably that she is?

quote:

benefit of the doubt and rule favorably

Its not clear whether its better for a given person (especially one who cannot be distinguished from a gentile) to be ruled Jewish, and thus subject to many restrictions, and having the capability to beget a mamzer, or to be ruled not Jewish, and thus exempt from all but the 7 Noachide laws.

But for a person who lives a Jewish life under the presumption of being Jewish, but a question, such as a discovered adoption without precise knowledge on the Jewish lineage, perhaps they can be given the benefit of the doubt as you say, and is given the opportunity to undergo a ritual conversion to remove all doubt - its a slightly different type of conversion, but the person takes on the restrictions of a convert, such as to not marry a Kohein.