A Cologne edition of 1669 stated that the Marquis de Chamilly was their addressee, and this was confirmed by Saint-Simon and by Duclos, but, aside from the fact that she was female, the author's name and identity remained undivulged.

The letters, in book form, set a precedent for sentimentalism in European culture at large, and for the literary genres of the sentimental novel and the epistolary novel, into the 18th century, such as the Lettres persanes by Montesquieu (1721), Lettres péruviennes by Françoise de Graffigny (1747) and Julie, ou la nouvelle Héloïse by Jean-Jacques Rousseau (1761).

The Letters of a Portuguese Nun were written in the same style as the Heroides, a collection of fifteen epistolary poems composed by Ovid, and "Lettres d'Héloise à Abélard", a medieval story of passion and Christian renunciation.

[1] They form a monologue beginning in amorous passion and slowly evolving, through successive stages of faith, doubt, and despair, toward a tragic end.

None of the arguments presented by Myriam Cyr, however, differs significantly from the 19th-century debate on the authenticity of the work, and the bulk of the critical evidence continues to favor[how?]