He said he knew mail would not blow out because he had tied rubber bands around the bundles.
Mr McLennan also said he had taken his phone out of his pocket at traffic lights because it was beeping, and pulled over at the earliest opportunity.
Despite this Mr McLennan was dismissed from his job.
Earlier this year an Employment Relations Authority determination found that NZ Post's investigation was insufficient to support the conclusions it reached.
The authority ordered NZ Post to pay Mr McLennan $5110 in lost wages and $4900 in compensation.
However, these amounts were reduced by 30 per cent, as the authority believed this was what Mr McLennan had contributed to the situation that led to his own personal grievance.
The authority declined Mr McLennan's wish to be reinstated to his old position, saying that given the emphasis on safety within NZ Post, his use of a mobile phone at traffic lights breached road rules and raised concerns over safety.
The authority's decision has since been challenged by Mr McLennan at the Employment Court.
He said it should not have concluded that the facts found warranted a reduction in remedies and a denial of reinstatement.
In a decision released this week, Judge Bruce Corkill agreed with the authority's conclusion as to the extent of Mr McLennan's contribution in respect of financial remedies.
However, he found that Mr McLennan was to be reinstated to his former position within 14 days after the date of the decision.
"There is no evidence that reinstatement would not be practicable... I find it reasonable in all the circumstances to order reinstatement.
A NZ Post spokesman said they accepted the Employment Court's ruling and would not be appealing the decision.