Darren Johnston, of Gleneagles in Cloughmills, County Antrim, targeted birthday cards containing money over a 14-month spell, a court was told.
The 29-year-old was told the scale of his breach of public trust warranted immediate imprisonment.
But the judge granted Johnston bail pending the outcome of an appeal against the jail term.
Johnston was convicted of stealing a total of £1,280 by opening packages due for delivery on dates between July 2013 and September 2014.
He also took two DVDs and a bank card from other parcels.
In addition to the thefts, he was also sentenced for six counts of interfering with mail.
Johnston has since lost his job as a Royal Mail postal operator.
A defence solicitor told Belfast Magistrates' Court that he acknowledged the seriousness of the offences.
"For those members of the public deprived of this money it was a disgrace," the solicitor said.
Johnston had come under financial pressure to support his family while his partner was off work, the court heard.
His £300 a week salary became "stretched" as he struggled with debts, the solicitor said.
"What he did thereafter was foolish, stupid and selfish," he added.
"He has made himself practically unemployable, and it's going to be a difficult road back."
Johnston is remorseful and wants to try to repay those he stole from, the solicitor added.
But the judge told Johnston: "You were routinely opening mail and targeting mail you thought contained money for gifts.
"I view this as a most serious breach of trust."
She added: "Nobody knows the financial means of the persons who were stolen from."
Johnston had pleaded guilty and his previous record was clear.
But the judge ordered him to serve six months in prison.
He was released from custody on £500 bail after his legal team confirmed its intention to appeal the sentence.
A postal worker who stole nearly £1,300 in cash gifts sent by mail has been sentenced to six months in jail.