If you fail to log in 3 times in a row, you are sure that your username and password are correct, then you should stop logging in and contact customer service.
Ask them if there is a problem with their server or with your account. Remember not to keep trying after several failures, this may cause your account to be closed or cancelled.

Parcel Send – Australia Post

Parcel Send – Australia Post

Australia Post

Enter your details to log in to your account. Email address. Password.

eParcel – Australia Post

Help & Support (Hotline hours are 8am–6pm, Monday—Friday; (Except national public holidays) Consumer Parcel Tracking Enquiry > Parcel Tracking > Click to track an item or access MyPost to track multiple deliveries across your devices. > Frequently Asked Questions > Click for answers to common tracking questions. > Customer Service > 13 POST (13 7678)

Login – MyPost Business – Australia Post

Login – MyPost Business – Australia Post

Sending – Australia Post

Sending. Send parcels and letters in Australia, or overseas, with Australia’s most trusted delivery service. Calculate postage & delivery times. Check stamp prices. Shop packaging. Print postage labels. Track an item. Track an item. Enter tracking number. e.g. AA123BB2234.