Is the mother of the person my mother breastfed considered a mahram?

Al-Bukhari and Muslim narrated from Ibn Abbas, may Allah be pleased with them both, that the Prophet, peace and blessings be upon him, said: "What is prohibited by lineage is also prohibited by suckling." However, scholars have made an exception to this rule regarding the mother of a brother or sister through suckling. The mother of your suckling brother is not considered one of your mahram, and it is permissible for you to marry her if there is no other reason for prohibition.