The postage rates. These rates are governed by the USPS. However they have negotiated discounts with services like Stamps.com to provide discounts of 5% - 10% off the standard rates for priority or express mail services. This can amount to some very nice savings depending upon your shipping volume.

So you definitely need to keep this type of thing in mind if you are looking for the cheapest online postage.

Fees. When you use online postage, you normally have to pay a monthly service fee of around $15. However some of the services like Stamps.com will sometimes start you off with discounts, postage, and a postal scale (check their website for their latest offers, which may or may not contain what we've mentioned). This way you can weigh the item yourself and then use the shipping software to determine the correct amount of postage required.

This can save you money in the long run since you don’t have to guess at the amount of postage required. Otherwise you will most likely apply too much postage or risk having the package or letter returned by not including enough postage on it.

Therefore a scale is an invaluable tool to have when trying to get the cheapest online postage. Check with the other online postage companies you might be considering to see if they provide you with a scale. Otherwise you will have to factor that extra cost into the true cost of the postage.

So you may find a service which has lower monthly membership fees but requires you to use a special printer or purchase a scale. This adds to the effective cost so definitely keep these kinds of things in mind..