How to write sorry for delay in mail

Here are a few examples of how you can write a polite apology for a delay in sending a mail:

Formal

Dear [Recipient's Name],

I am writing to apologize for the delay in sending you the [mail/package/document] that was due to be sent on [original expected date]. Unfortunately, unforeseen circumstances [briefly mention the reason for the delay, e.g. "technical issues" or "unforeseen circumstances"] caused a delay in our processing and shipping of your item.

Please be assured that we are working diligently to rectify the situation and your [mail/package/document] will be sent to you as soon as possible. We estimate that it will arrive on [new expected date]. If you have any questions or concerns, please do not hesitate to contact us.

Once again, we apologize for the inconvenience this delay may have caused and appreciate your patience and understanding.

Sincerely, [Your Name]

Informal

Hi [Recipient's Name],

I wanted to reach out and apologize for the delay in sending you the [mail/package/document] that was supposed to arrive on [original expected date]. Unfortunately, we encountered some unexpected issues that slowed down our processing and shipping.

I want to assure you that we're working hard to get your item to you as soon as possible. We expect it to arrive on [new expected date]. If you have any questions or concerns, please don't hesitate to get in touch.

Thanks for your understanding and patience.

Best regards, [Your Name]

Email template

Subject: Apology for Delay in Sending [Mail/Package/Document]

Dear [Recipient's Name],

I am writing to apologize for the delay in sending you the [mail/package/document] that was due to be sent on [original expected date]. Unfortunately, unforeseen circumstances [briefly mention the reason for the delay] caused a delay in our processing and shipping of your item.

Please be assured that we are working diligently to rectify the situation and your [mail/package/document] will be sent to you as soon as possible. We estimate that it will arrive on [new expected date]. If you have any questions or concerns, please do not hesitate to contact us.

Once again, we apologize for the inconvenience this delay may have caused and appreciate your patience and understanding.

Best regards, [Your Name]

Remember to customize the apology letter or email to fit your specific situation and relationship with the recipient.