Learn Farsi: نامه‌ها با پیک فرستاده می‌شدند.

It combines the past participle of the main verb, فرستاده (sent), with the past continuous form of the auxiliary verb شدن (to become), which is می‌شدند (they were becoming). Together, they literally mean 'they were becoming sent,' which translates to 'they used to be sent' or 'they were being sent.'

نامه‌ها (letters) is an inanimate plural. Why does the verb می‌شدند have a plural ending instead of being singular?

In Farsi, inanimate plural subjects like نامه‌ها usually take a singular verb. However, using a plural verb is also grammatically correct. It is often done in formal writing or to emphasize the individual items rather than treating them as a collective group. Here, می‌شدند instead of می‌شد simply sounds a bit more formal.

The translation says 'used to be sent.' Can فرستاده می‌شدند also mean 'were being sent'?

Yes! The past continuous tense in Farsi (formed by adding the می prefix to a past tense verb) is used for both habitual past actions ('used to be sent') and ongoing past actions ('were being sent'). You would rely on the surrounding context of the conversation to know which one is meant.

I thought با meant 'with.' Why does the English translation say 'by courier'?

While با primarily means 'with,' it is also widely used to indicate the means or method of an action, similar to 'by' in English (like traveling 'by' train, or sending something 'by' courier). In more formal passive sentences, you might also see (by means of / via) used to introduce the agent.