avoid gmail block my mails for sending invoices

Avg Bid (USD)
Project Budget (USD)
$30 - $40

Project Description:
i need a way that gmail does not block my mails which are sent automatically ( about 30 invoices to customers only)

i got some information about identification and authorization. but i have no idea what to do!

Skills required:
Email Marketing, Google App Engine, Google Go
Hire veroca01
Project posted by:
veroca01 Austria
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