Brian, it will not come registered mail. Watch your mail over the next week to make sure it does not get lost in the holiday junk mail. if you are rolling your 401(k) assets into an IRA and they are mailing the check to you for you to deposit into your new custodian, you only have 60 days to deposit that check into an IRA to avoid 100% taxable distribution. Otherwise, that lump sum dollar amount is considered 100% income in 2014, plus you may have a 10% penalty if you are younger than 59 1/2. Hope this helps.
Did you process a rollover or are you receiving a full distribution? If you are rolling it over to an IRA, those sometimes get sent directly to the firm and can vary from 5 to 10 business days. Same time frame in most cases if they check comes to you, it most likely will not be sent registered mail.
When you request a lump sum payout, the investment custodian may send a check directly to you, or if you have a Rollover IRA and you have specified an account number, then they might send the funds to whichever investment firm you are using to manage your Rollover IRA. Your check will probably arrived via overnight mail, unless you requested regular or registered mail. I agree with Nicholas's above...you might receive it within 7 to 10 business days.