I’m also wondering about this connection - a lot of black people refer to their moms as mam. Mommy, directly, but also mam, as in yes, mam. Could that come from mammy? It’s all so mysterious and yet it actually happened. We need someone to invent a real time machine.
The odds are, IMHO, that “mam” is actually “ma’am” which is a variant of “madam” and which is used as a term of politenes to any female, just as “sir” is used to males. It’s a generic term in all levels of “polite” society. It’s considered polite to say, “Yes, Ma’am” and “Yes, Sir” instead of “Yeah.” If those terms are indeed unfamiliar to you then perhaps a look at other terms of politeness (which may be on the way out of common parlance) could add to your understanding.
Terms of politeness are not unfamiliar to me, thank you. I also speculated that mam is actually ma’am, the letter e elided. But it may not be that such a direct connection exists, even as apparent as it may be.