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You can certainly ask for leniency but in my experience unless you have a compelling reason that is deserving of compassion or proves that you were completely not at fault for failing to receive your mail you are unlikely to have the fine waived.
If you think you can mount a credible argument first try writing to the agency that issued the fine as they will usually have guidelines as to when they can or should withdraw a fine.
Failing that you can apply to the court either to find you not guilty, if you think you have done nothing wrong, or to ask for a lesser fine if you think there extenuating circumstances that would justify a reduction in the fine (such as you are on a low income, or have a serious illness which impacts your ability to pay a fine, etc). Your prospects in court can be uncertain however, and if the court is unimpressed with your reasons for contesting the matter before the court, it can in fact increase the fine, so this is a risky option that should only be considered if you have a compelling reason for pleading not guilty or asking for a reduction.
I trust the above assists your understanding.
Good luck and please rate my answer.