The Middle Ages Galaxy Properties with Integral field spectroscopy (MAGPI) survey is a Large Program on the European Southern Observatory Very Large Telescope using the Multi Unit Spectroscopic Explorer (MUSE) instrument. This paper presents the data release for the MAGPI emission-line products and includes emission-line maps for 836 galaxies at $0.05\le z_\mathrm{spec}\le 0.424$ ($\mathrm{H}\alpha$-window) and aperture-based emission-line measurements for 2607 galaxies at $0.05\le z_\mathrm{spec}\le 1.50$ (upper bound is [O II] cut-off), both based on the GIST software, for all 56 MAGPI fields. We use these data to examine dust attenuation, which represents a major source of uncertainty in the derived properties of galaxies that are critical to constrain models of galaxy evolution. We examine the role that the spectroscopic aperture covering fraction ($f_c$) has on the relationship between the Balmer decrement ($\mathrm{BD}=F(\mathrm{H}\alpha)/F(\mathrm{H}\beta)$; a common proxy for dust attenuation) and the total stellar mass ($M_\star$). Several studies have suggested that the BD--$M_\star$ relation may be redshift invariant; however, the compared surveys often have different $f_c$ due to their differing fibre or slit sizes that can cause systematic offsets. Our results indicate that $f_c$ has a significant impact on this relationship, due to galaxies having negative BD radial gradients, which are more negative for more massive galaxies at $z\lesssim 0.4$. Comparing spectroscopic surveys with $\langle f_c\rangle \gtrsim 0.5$, we find that the BD--$M_\star$ relation shows a preference for redshift evolution and is roughly consistent with the behaviour of ultraviolet stellar continuum attenuation redshift evolution ($A_\mathrm{FUV}$-z), with the average dust attenuation in galaxies peaking at $z\sim 1.2$ and decreasing at lower and higher redshifts.