Royal Mail's overall revenue grew by 2% in the nine months to 24 December.
Parcel revenue rose by 4% and volumes increased by 6%, with 149 million parcels handled over the December trading period.
Letters revenue fell by 3% and volumes declined by 5%.
General Logistics Systems (GLS) volumes and revenues rose by 10%. Excluding the impact of the timing of Easter and other public holidays across Europe, underlying volume and revenue movements would have been around 3 percentage points higher.
For the full year, the group expects parcels performance to be broadly in line with the performance in the first nine months as it continues to make improvements to its network and services. Addressed letter volumes (excluding political parties' election mailings) are expected to be in the middle of the range of 4-6% decline for the full year.
In GLS, underlying revenue growth for the full year is expected to be broadly in line with the first half. However, Royal Mail said it is continuing to see cost pressures due to labour market conditions in many of GLS' European markets, as well as in the US, which may slightly impact margins this year.
The group's cost avoidance programme is on track to deliver around £190m of UKPIL operating costs avoided in 2017-18. Transformation costs will be around £130m for the full year.
Moya Greene, chief executive officer of Royal Mail, said: "We have continued to make progress in talks with our unions on pay, pensions and the other issues under discussion. We have agreed the fundamental principles on some of the key issues and talks are ongoing to finalise these and other areas. We believe we can reach agreement on an affordable and sustainable pension solution and a pay deal that will enable us to continue to innovate and grow."