You shall receive an email if your email addres is written in the addres line of email.
If you read email, intranet, internet, of the company may have the option of read and receipt, and sender would have a message of confirmation by email.
If you do not agree to any change/updation/adittion/deletion in the term of contract of employemnt, or manner of communication,you should always respond/reject in writing, and obtain acknowledgment for your record.
You can respond by email
or
by a letter addressed to the appointing authority or sender, and obtain acknowledgment under seal and signature from the desk where all mails and letters of the company are received.It is believed you know this and obtain a copy.
Companies increase the notice period, when they do not want to loose employees to the competition,deter the employees and check attrition and retain headcount, and decrease the notice period, when they have tested most of the employees and have decided to replace or have decided to reduce the headcount and resort to terminations if required.
Don't resort to excuses which shall have no acceptance, rather be smart.
Business climate has changed, and compaies do not marry employees, and employees do not marry companies. Be a good professional,human being, gentle and keep moving.