Please accept my apologies for the delayed response.
Kindly accept my sincere apologies for the delay in replying to your e-mail.
My sincerest apologies for not getting back to you about (THE REASON FOR YOUR EMAIL) sooner.
Sorry for the late response.
Thank you for your patience while I was working on (THE REASON TO DELAY THE RESPONSE) I sincerely apologise for the delay in response.
I understand that you would have preferred an earlier response to your inquiry, but your request required some time.
I am really sorry for the delay in responding to this.
I apologise for the delay response. I was out for a few days due to health issues.
Once again, please accept our sincere apologies for causing you such inconveniences and delaying you so much in time.
Sorry for the delay in coming back to you, it has taken time for me in order to clarify the issues within our departments.
Please note that we are a bit high overloaded nowadays and maybe there will be some delays in the response.
I am apologizing in advance!
Please accept our apologies for the delays caused by some internal re-organizations.
First off, please accept my apologies for the delay in coming back to you.
The recent acquisitions and internal re-organizations have led to an exceeded workload and a backlog at our end.
We appreciate your business and we apologize for the late response. This is an unexpected delay due to our workload but please note that this will not happen again.
Please forgive us for this delay caused by some internal re-organizations. Any delays are certainly unintentional and regrettable. We have taken actions to clear this issue and it’s not going to happen again.
I am extremely sorry for the late response. I had issues with my Outlook and I just received your email.