Gmail allows you to block someones from your Android, The following steps are:
Open your Gmail and enter your login details.
Open an email from that person you want to block.
Click on the “three dots” at the top right corner on the screen.
After that, select the block option to block the person.
Then confirm the block to proceed.
Source: https://webmailup.com/how-to-block-someone-on-gmail/