If your mailing system is not sealing envelopes correctly, the issue is usually related to envelope placement, sealing fluid, envelope condition, flap style, or the sealing section of the machine.
MCC supports Quadient mailing systems. While the exact design may vary by model, most sealing issues can be checked with a few basic steps before requesting service.
Common Signs of a Sealing Problem
You may have a sealing issue if:
- Envelopes come out completely unsealed
- Only part of the flap seals
- Flaps are wet but not sticking
- Flaps are dry after running through the machine
- Envelopes are sealing unevenly
- Envelopes are getting wrinkled or damaged
- The machine feeds envelopes but does not moisten the flap
Step 1: Check the Sealing Mode
Some mailing systems allow you to turn sealing on or off.
Before troubleshooting further, confirm the machine is set to seal envelopes. Look for a sealing option, sealer setting, or moistening mode on the control panel.
If sealing is turned off, the machine may still feed and print postage but will not moisten the envelope flap.
Step 2: Check the Sealing Fluid
If your mailing system uses sealing fluid, make sure the reservoir has enough fluid.
Low or empty sealing fluid can cause envelopes to come out dry or only partially sealed.
Check that:
- The sealing fluid reservoir is filled
- The correct sealing fluid is being used
- The reservoir is seated properly
- Fluid is reaching the moistening area
- There are no visible leaks
Do not use random liquids, tap water, or homemade mixtures unless your machine’s instructions allow it.
Step 3: Check Envelope Flap Position
Envelopes must be loaded in the correct direction for the machine to moisten and seal the flap.
Make sure:
- Envelopes are facing the correct direction
- Flaps are positioned as required by the machine
- Flaps are not tucked, folded, or already sealed
- The stack is aligned before feeding
- All envelopes in the stack face the same way
If envelopes are loaded incorrectly, the machine may process the mail but miss the flap entirely.
Step 4: Check the Envelope Type
Not all envelopes seal equally well in a mailing system.
Sealing problems may happen with envelopes that are:
- Too thick
- Overstuffed
- Curled
- Wrinkled
- Damp
- Old or dried out
- Glossy or coated
- Unusual in size
- Designed with non-standard flaps
- Poorly manufactured
- Self-seal or peel-and-seal style
Some envelope adhesives do not respond well to machine moistening, especially if the envelopes have been stored for a long time or exposed to humidity.
Step 5: Avoid Overstuffed Envelopes
Overstuffed envelopes may not pass through the sealing section evenly.
If the envelope is too thick, lumpy, or uneven, the flap may not make proper contact with the moistening or sealing area.
Try running a few standard, flat envelopes through the machine. If standard envelopes seal correctly but stuffed envelopes do not, the issue is likely the envelope thickness or contents rather than the machine.
Step 6: Check for Stuck or Damaged Flaps
Before loading envelopes, inspect the stack.
Remove envelopes with:
- Bent flaps
- Torn flaps
- Flaps stuck to neighboring envelopes
- Uneven folds
- Glue already exposed
- Moisture damage
- Thick inserts preventing the flap from closing flat
Fan the stack lightly and align the edges before loading.
Step 7: Check the Moistening Area
If the machine is set to seal and has fluid, the moistening area may need attention.
Depending on the model, the sealing section may include a brush, wick, sponge, pad, or moistener assembly. If this area is dirty, dry, clogged, or worn, envelopes may not seal properly.
Look for:
- Dried adhesive buildup
- Paper dust
- Debris
- Dry moistening parts
- Uneven fluid contact
- Damaged or worn sealing components
Use only approved cleaning methods for your mailing system. Do not scrape parts with sharp tools or pour fluid directly into the machine.
Step 8: Run a Small Test Batch
After checking the settings, fluid, envelope placement, and envelope condition, run a small test batch.
Use clean, standard envelopes that are not overstuffed.
Confirm that:
- Envelopes feed straight
- Flaps are moistened
- Flaps close completely
- The seal holds after a few seconds
- Envelopes are not wrinkled or damaged
If the test batch seals correctly, the original envelope stack may be the issue.
Step 9: Let the Seal Set
Some envelopes may need a few seconds for the adhesive to bond after being moistened.
If the flap is wet but opens immediately, press it closed and wait briefly. If the seal still does not hold, the envelope adhesive may be old, weak, or incompatible with machine sealing.
When to Contact MCC
Contact MCC if:
- The machine is set to seal but envelopes remain dry
- Sealing fluid is full but not reaching the flap
- Envelopes are sealing only on one side
- Standard envelopes do not seal correctly
- The moistening area appears damaged
- The machine leaks sealing fluid
- Envelopes are being wrinkled or damaged
- The same problem continues after checking envelope placement and fluid
- The machine shows an error message
What to Include in Your Service Request
When requesting service for envelope sealing problems, include:
- Business name
- Contact name
- Phone number
- Mailing system model
- Serial number
- Equipment location
- Description of the sealing issue
- Envelope size and type
- Whether the issue happens with all envelopes or only one batch
- Whether sealing fluid has been checked or refilled
- Any error message shown on the machine
- Photos of the envelope, flap, or machine screen, if helpful
The easiest way to request service is by using the MCC Express Passport, if one is available for your mailing system. You can also contact MCC by phone or email.