According to the MASS gov website,
https://www.mass.gov/info-details/mass-general-laws-c62-ss-2#(a)-
you can exclude the portion of dividends from a fund (RIC) that represent interest from EITHER Mass gov OR US government obligations. ( Sec. 2(a)(2)(J), Ch. 62, G.L.).
For the US gov case 2(A) says:
"... dividends received from a RIC ... to the extent such dividends are attributable to interest on obligations of the United States exempt from state income taxation ...". So, interest you receive from US gov obligations you hold are exempt (and show up in a numbered 1099 box), as well as the portion of dividends from a fund that are from interest on US obligations. Each fund that falls into this category will (should) provide (somewhere) the exact percentage of its dividend distribution that comes from state tax exempt sources. Each fund company should provide a year end document of this. For example, for Fidelity funds, they supply this here
"2023 Percentage of Income from U.S. Government Securities"
https://www.fidelity.com/bin-public/060_www_fidelity_com/documents/TY23-GSE-Supplemental-Letter.pdf
Note the above table for the most part identified funds by their ticker with some exceptions (e.g. "Fidelity® Government Money Market Fund - All Classes* .. so SPAXX ) so if you don't find your funds symbol also search this table by fund name).
In addition a fraction of dividends could also be from obligations which are exempt from state tax too. When the fraction is state specific then there's no way to characterize this in one of the numbered 1099-DIV boxes.
https://www.fidelity.com/bin-public/060_www_fidelity_com/documents/taxes/2023-tei-by-year.pdf
Be sure to check all your funds, not just money market type, since many stock funds include a portion of their holding in US obligations. The fractions might not be large for generic funds, but ever little bit helps!
