Selling through email
In the name of Allah, the most Beneficent, the most Merciful.
The definition of sale (bay) is the exchange of an owned commodity for another in a specified manner or the exchange of an owned commodity for another in a beneficial and special manner. (Badaaius Sanai p.133 v.5)
The primary cornerstone of a sale for the Hanafi’s is the offer and acceptance or any other mechanism, which signify exchange. In the Hanafi Fiqh, offer is the action of one of the two parties indicating willingness to engage in a transaction. The offer thus originates from the buyer or the seller and acceptance is indicated by the second party. The offer is defined as the primary action and acceptance as the secondary one, regardless of whether they originate with the buyer or the seller. (Fathul Qadir p.74 v.5)
With regards to your question when the offer and the acceptance have been completed, it is not permissible to break the transaction even though if it was agreed over the internet. However, through mutual consent, the buyer and seller can annul the transaction. This is known as ‘Iqalah’.
Saaiduna Abu Hurairah Radiallahu Anhu narrates that the Prophet of Allah Sallallahu Alahi Wasalam said ‘Whoever revokes the sale of someone who regrets it, Allah will revoke his sins on the Day of Judgment.’ (Sunan Baihaqi)
Only Allah Knows Best
Mohammed Tosir Miah
Darul Ifta Birmingham