Whether leaving or not, discreetly untangle your personal business from your employer's IT systems. (Perhaps your Earnings Statements, annual W-2, and other vital communications are going to a company email address that you will lose.) Takes several months. Applies no matter where you work, what your job situation, or how innocent your activities. 

Important personal emails may be discarded as spam or phishing by your employer's firewall. The email accounts, files, and backups all legally belong to your employer, not to you. The company IT department may close your email account or remotely wipe your company PC -- at any time without warning.

This is based on personal experiences -- at various employers -- reported by members.

Lost messages. If your employer's automated email monitoring system blocks some of your emails for any reason -- or when you retire or otherwise leave your employer -- messages will not reach you. Senders may not be notified -- or may receive a reply that looks like phishing or is ambiguously-worded (for example, "User unknown in virtual alias table.") This may be interpreted unfavorably by the sender. 

Loss of personal data. Members report losing their address books, personal contact lists, and personal files (such as the records of a non-profit they worked with) due to their employer unexpectedly collecting their notebook -- or IT, management, or other employees removing equipment from their office in their absence. Passwords are irrelevant -- by the time they found out, their hard drive had been wiped clean. Many companies now have the ability to access company PCs and mobile devices remotely. Your data can be wiped while the equipment is still in your physical possession.

Privacy. You have no legal expectation of privacy -- or data reliability -- when you use your employer's IT facilities.

"If you’re using an email account provided by your employer, an administrator with qualifying credentials can typically access all your incoming and outgoing emails on that account, as well as any documents you create using your work account or that you receive in your work account. This allows companies to review emails as part of internal investigations and access their materials after an employee leaves the company. A company may also search through and read employee emails after receiving a subpoena, if the company itself is under investigation, or if it’s reviewing information to prepare for litigation."  --Consumer Reports

Extreme example: 600,000 Enron employee emails were made public as a result of a legal investigation -- love notes and all.

Timing when you leave. Even if you retire or leave on good terms with your employer, your access to company systems and your company email account may stop well before your last hour. Cases have been reported where access stopped -- without warning -- on the day before the last day... or even weeks earlier. Any autoreply that you set up will probably be immediately disabled. Assurances from managers have proven to be irrelevant -- your manager has no control over the automated HR and IT processes.

"I ran into a problem obtaining the SKU number because the email that HP originally sent me with that info was to my work email address and I had retired just the day before; thus my account had already been locked down and I never gained access to the email."

Untangling your personal business from your employer's IT systems takes several months.

Your account on the company email system

If you have any personal correspondence directed to your email account at work, you must change this.

Wherever you work, it is a bad idea to use your company email address for your personal email:

- You run the risk of losing your account connections -- including not only critical ones (like those with your health providers or your financial institutions) but also seemingly-trivial ones that can be a hassle to straighten out, like the public library or Netflix. It can be very difficult to recover access to social media accounts such as Facebook or LinkedIn when you don't have access to the email address on the account. You can also lose your personal address book.

- An unfortunate email subject line (or sender name) may be visible on your desktop or notebook screen while you are talking to someone or making a presentation.

- Unsolicited spam or an ill-advised joke may trigger the monitoring system that most corporations use to prevent "hostile work environment" lawsuits, leakage of intellectual property, business conduct violations, or other legal issues. 

Even if you don't plan to leave your employer, you should move any personal email activity and directory entries out of your company email account.

LinkedIn: You can have multiple email addresses on your LinkedIn account. LinkedIn sends job leads, requests to connect, and some Group emails to your primary address. For most people, the primary address should be a personal email address. This maintains continuity through changes in employment, provides privacy, and avoids important emails being inadvertently discarded by an employer's firewall. In addition to your current work address, you can include former personal and work addresses on your account as secondary addresses -- so that LinkedIn members who know you by another address will be able to connect with you..

After your last day, your employer's email system will say that it has never heard of you 

However you left, any email autoreply that you have set up will be probably be immediately disabled.

People who send you email will either receive no reply -- or your ISP will forward your former employer's error message to them.
For example, HP sends this ominous reply: "Recipient address rejected: User unknown in virtual alias table."
Because your former employer's reply looks like spam or junk, it may not reach your correspondent at all.

How to switch your personal email

You must start now -- this normally takes a couple of months.

If you have time to switch... Once you have your new account set up, you can watch your incoming email and change addresses with businesses and people. After a few months, you will have switched over the stuff you really want.

If you don't have months to switch... Search your email for correspondence related to banking, e-commerce such as Amazon, friends, etc.

If you have any personal correspondence directed to your email account at work, notify the people and businesses you correspond with ASAP. Change account settings for services -- including internal services like the employee purchase discount program.

Create a spreadsheet with a list of all websites that you have accounts on that are registered to your company email address so you can keep track. Prioritize accounts (such as financial accounts) that you need to change before you lose access to your company email account.

It is best to change all accounts before you lose access to your company email account. Most websites will allow you to change your email address at any time -- if you know your password. However, if you don’t remember your password for a given site, you’ll need to reset it from your old email account before you lose access. And there are exceptions -- for example, craigslist -- that require access to your old email account in order to authorize an email address change.

You must allow time for this lengthy and tedious process-- most such changes require you to confirm by replying to an email sent to your old address.

How to set up a professional email account

Advice from members on getting a private, professional email account on Microsoft, Google, Yahoo, or Apple -- and choosing a professional email username, go here: How to set up professional email.

If you wish, you can have your personal email address forwarded to your email address at your employer. But company email systems often have crude anti-spam mechanisms that reject email newsletters you signed up for -- and you still have the privacy and data-loss issues.  

Files on the company computer

Whether or not you are leaving your employer, make copies of any personal files on your PC, take them home, and use your personally-owned computer for that work.

Members point out that just copying .pst files will not copy anything located on the central Exchange server -- Tasks, Contacts, Notes, Calendar items, personal emails.
To retrieve your personal items, you must:
1. Create a new .pst file for personal information. See
http://office.microsoft.com/en-us/outlook-help/create-an-outlook-data-file-pst-to-save-your-information-HA010355677.aspx
2. Copy your Tasks, Contacts, Notes and Calendar folders and any personal messages in your Inbox to the new .pst file.
3. Copy this .pst file and any other .pst files containing personal information to a thumb drive.