New Zealand Post says most of its Kiwibank shops in Christchurch will be closed on Tuesday and the city's mail services may be disrupted.
There have been more significant quakes in Canterbury causing damage, including tremors measuring 6.0 and 5.5 on Monday.
Eighteen of the city's 27 Postbank and Kiwibank stores will not open on Tuesday morning as damage is assessed, but some stores may re-open later in the day.
Staff were evacuated from the Orchard Road mail processing centre on Monday afternoon as a precaution.
New Zealand Post says deliveries may be interrupted on Tuesday as a result of the evacuation and will only go ahead if it is safe for posties to deliver the mail.
Courier services will still operate, but may also face delays.