quando spedisco la newsletter alcune email mi tornano indietro nella mia mailbox
con una scritta del genere

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These recipients of your message have been processed by the mail server:
esempio@esempio.it; Failed; 4.4.7 (delivery time expired)

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oppure

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does not like recipient.
Remote host said: 553 sorry, no mailbox here by that name. (#5.1.1)
Giving up on

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o anche

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failed after I sent the message.
Remote host said: 554 delivery error: dd Sorry your message to esempio@yahoo.com cannot be delivered. This account has been disabled or discontinued [#102].

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secondo voi si tratta di indirizzi inattivi ?