This paper endeavours to understand the effects of incarceration on the maintenance of family ties through letters. 19th century regulations defined a list of family members permitted to write to prisoners. In doing so, these rules established family norms that gave precedence to legal kinship to the detriment of other ties that were harder to prove. Moving from the regulatory framework to its appropriation by prisoners, however, shows that maintaining ties was not just a matter of compliance with the regulations. The gendered distribution of family roles shaped letter-writing relationships in prison. Female prisoners had to cope with a twofold constraint. The social stigma surrounding their convictions was even greater than for men. But, as mothers, wives or sisters, they remained at the forefront of the letter-writing relationship. The latter was constantly weakened by incarceration: supervision by the administration raised the threat of censorship, while the prison sentence itself transformed the letter into a precarious and fragile place of expression for a community of suffering and humiliation beyond the prison walls.